Non-rigid Part Research Articles

A numerical-tensorial "hybrid" nuclear motion Hamiltonian and dipole moment operator for spectra calculation of polyatomic nonrigid molecules.

The analysis and modeling of high-resolution spectra of nonrigid molecules require a specific Hamiltonian and group-theoretical formulation that differs significantly from that of more familiar rigid systems. Within the framework of Hougen-Bunker-Johns (HBJ) theory, this paper is devoted to the construction of a nonrigid Hamiltonian based on a suitable combination of numerical calculations for the nonrigid part in conjunction with the irreducible tensor operator method for the rigid part. For the first time, a variational calculation from abinitio potential energy surfaces is performed using the HBJ kinetic energy operator built from vibrational, large-amplitude motion, and rotational tensor operators expressed in terms of curvilinear and normal coordinates. Group theory for nonrigid molecules plays a central role in the characterization of the overall tunneling splittings and is discussed in the present approach. The construction of the dipole moment operator is also examined. Validation tests consisting of a careful convergence study of the energy levels as well as a comparison of results obtained from independent computer codes are given for the nonrigid molecules CH2, CH3, NH3, and H2O2. This work paves the way for the modeling of high-resolution spectra of larger nonrigid systems.

Feasibility of new types of technological equipment in the manufacture of nonrigid flat aluminum parts

In this work, we assess the efficiency of the SCHUNK VERO-S Aviation clamping system in manufacturing nonrigid aluminum parts in comparison with the existing technology of their small-scale production at domestic aircraft plants. The research was conducted using the facilities of mechanical shops that manufacture nonrigid aircraft parts to estimate the time and economic expenditures involved in their production when changing the cutting mode and machining allowances. The proposed technological process was implemented by the HALTEC Russian engineering company at an aircraft manufacturing plant of the Russian Federation. The duration of the technological process amounted to a total of 14 hours, with the existing production technology lasting for 300 hours. The process duration was reduced by eliminating two thermal stabilization operations and shortening the machine-setting time by 50%. The machine-setting time was reduced by increasing the number of cutting mode elements during manufacturing of a non-rigid aluminum part using this tooling, as well as by using a modified machining strategy. The use of the SCHUNK VERO -S Aviation system together with a modified machining strategy for a thin-walled non-rigid workpiece allows for an almost complete compensation of deformations caused by residual stresses of the first kind. The new modern technology of SCHUNK VERO -S Aviation proves to be effective for the small-volume and series production of thin-walled nonrigid components of the required quality without warping, multiple straightening operations, thermal and temporal stabilization.

Calculation of the deflection of the blade of the disk of an axial gas pumping machine

The mechanism of occurrence of errors leading to failure of parts of compressors and pumps is investigated. A method is proposed for non-destructive control of the accuracy of manufacturing of non-rigid parts with end surfaces of revolution without reducing productivity. Keywords: compressor, non-rigid part, technological system, diagnostics. nga112001@list.ru

On the perception and handling of deformable objects – A robotic cell for white goods industry

• Design and implementation of a robotic system for the manipulation and assembly of linear non-rigid components. • Multi-sensor system for flexible part cognition and safe human-robot interaction. • Dexterous gripper for non-rigid material manipulation. • Control framework for process coordination and safe human -robot collaboration. • Validation and testing in a white goods industry case study. Advancements in mechatronics, perception and computational methods allowed robotics to focus on non-rigid part manipulation, which is characterized by high complexity due to the unpredictable and compliant behavior of flexible materials. This paper presents the automation of a manufacturing process involving linear non-rigid components through the implementation of a robotic system that addresses challenges related to flexible material perception and handling. The corresponding technological approach consists of five steps namely safe material supply, detection, grasping, cross section recognition, and assembly. The proposed robotic cell comprises: (1) a multi-sensor system for flexible part recognition and safe human-robot interaction (2) a collaborative robot equipped with a dexterous gripper for flexible material manipulation, and (3) a control framework for process coordination. The robotic system has been tested on a case study originating from the white goods industry, where rubber gaskets are manipulated and assembled on household appliances. Experimental results proved that the implemented robotic system can tackle the challenges of flexible material manipulation with great consistency in the aspects of robustness and repeatability.

Automatic identification method of rigid sub-chains based on branch chain disassembly and replacement

The existing methods of rigid sub-chain identification are mostly based on calculating the degree of freedom (DOF) of the basic loop, the loop combination, and the special branch chain, for which efficiency and accuracy are generally difficult to combine. Therefore, this paper proposes a rigid sub-chain identification method based on the disassembly and replacement of the branch chain, with the core idea of eliminating the non-rigid sub-chain part in the kinematic chain (KC) to highlight the rigid sub-chain part. First, the two-degree chains of length greater than 1 in the KC topology is disassembled. Second, the characteristics of quadrilateral loops are studied, and the quadrilateral loops with a diagonal connection are replaced equivalently to realize further disassembly. Finally, the special edges of the remaining sub-graphs are analyzed and removed. Through the above steps, if topology is eliminated, the structure is reasonable; otherwise, topology contains a rigid sub-chain. This method is used to identify a non-isomorphic KC atlas, and a complete set of planar non-fractionated KCs with simple joints within six loops and 3-DOFs is obtained.

Assembly variation analysis of the non-rigid assembly with a deformation gradient model

PurposeThis paper aims to develop a mathematical method to analyze the assembly variation of the non-rigid assembly, considering the manufacturing variations and the deformation variations of the non-rigid parts during the assembly process.Design/methodology/approachFirst, this paper proposes a deformation gradient model, which represents the deformation variations during the assembly process by considering the forces and the self-weight of the non-rigid parts. Second, the developed deformation gradient models from the assembly process are integrated into the homogenous transformation matrix to model the deformation variations and manufacturing variations of the deformed non-rigid part. Finally, a mathematical model to analyze the assembly variation propagation is developed to predict the dimensional and geometrical variations due to the manufacturing variations and the deformation variations during the assembly process.FindingsThrough the case study with a crosshead non-rigid assembly, the results indicate that during the assembly process, the individual deformation values of the non-rigid parts are small. However, the cumulative deformation variations of all the non-rigid parts and the manufacturing variations present a target value (w) of −0.2837 mm as compared to a target value of −0.3995 mm when the assembly is assumed to be rigid. The difference in the target values indicates that the influence of the non-rigid part deformation variations during the assembly process on the mechanical assembly accuracy cannot be ignored.Originality/valueIn this paper, a deformation gradient model is proposed to obtain the deformation variations of non-rigid parts during the assembly process. The small deformation variation, which is often modeled using a finite-element method in the existing works, is modeled using the proposed deformation gradient model and integrated into the nominal dimensions. Using the deformation gradient models, the non-rigid part deformation variations can be computed and the accumulated deformation variation can be easily obtained. The assembly variation propagation model is developed to predict the accuracy of the non-rigid assembly by integrating the deformation gradient models into the homogeneous transformation matrix.

A CAD model for the tolerancing of mechanical assemblies considering non-rigid joints between parts with defects

During the design stage, the ideal simulation and visualization of the mechanical assemblies behavior require the modeling of parts with dimensional and geometrical defects. However, the deviations caused by parts deformations can generate an important difference between the ideal assembly and the real product. In this regard, this paper proposes a tolerance analysis method of CAD assemblies considering non-rigid joints between parts with defects. The determination of realistic rigid components with dimensional and geometrical defects is based on the worst case tolerancing approach and the Small Displacement Torsor (SDT) parameters. The Finite Element (FE) computation is executed to determine deformations of realistic non-rigid part models under external loads. Sub-algorithms to define non-rigid joints between realistic parts are developed. The tolerance analysis is established using the realistic CAD assembly. A case study is presented to evaluate the proposed model.

Computer-Aided Design/Tolerancing Integration: A Novel Tolerance Analysis Model of Assemblies With Composite Positional Defects and Deformations of Nonrigid Parts

Abstract Nowadays, the tolerancing integration in computer-aided design (CAD) tools remains among the major goals of mechanical manufacturers. In the virtual product development, ideal and rigid models are used in the digital mockup (DMU). Hence, research works developed integrated CAD models for tolerance analysis, while considering manufacturing defects. However, the tolerance analysis in the case of composite positional tolerance for feature patterns, commonly used in the industry, becomes a difficult activity with the consideration of parts deformations. Thus, this paper presents a novel CAD model for the tolerance analysis considering composite positional defect of features set and nonrigid component deformations due to external mechanical loads. The modeling of rigid components with dimensional defects is established based on the numerical perturbation method. Indeed, the relationships between driving and driven dimensions are determined to obtain the configurations in maximum and least material of the CAD model. Thereafter, the geometrical deviations are modeled by face displacements. The modeling of composite positional errors is performed while respecting the feature relating position tolerance zone framework and the pattern-location tolerance zone framework constraints, as well as the maximum or least material condition. The deviations caused by nonrigid part deformations are considered by the integration of finite element results into the CAD model. The realistic configurations of the assembly are obtained after the updating of mating constraints between rigid and nonrigid parts with defects. The composite positional tolerance is analyzed with the simulation of relative motion between parts. A case study is proposed to evaluate the developed tolerancing method.

Early Stage Variation Simulation and Visualization of Compliant Part Based on Parametric Space Envelope

Compliant, nonrigid parts are widely used in many industries today. Existing variation simulation analysis on the manufacturing part focuses on orientation and position deviation with part shape errors being largely omitted. This is a valid approach for the rigid part, but it is unrealistic and can be problematic for the compliant part. In this study, a new methodology has been introduced to compliant assembly early phase design to generate various probable variated manufacturing parts that conform to predefined tolerance specification or meet the certain industrial requirement. The proposed method is based upon the novel idea of a parametric space envelope, a purpose-designed variation tool constructed from parametric curves. Variation of embedded manufacturing part is linked to and controlled by a compact set of envelope’s boundary control points. Part variation instances are generated by simulating the control points’ movement in a systematic and efficient way. Importantly, simulated variations can be visualized in 3-D virtual space to provide user insight into part variation. The proposed methodology can help identify assembly high-risk regions, select proper fixtures, guide assembly engineering changes, and optimize assembly operations. An industrial case study on a deformable vehicle door hinge plate is presented to illustrate the methodology. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This article is motivated by two acute problems encountered in geometric variation simulation analysis for compliant parts in the early design stage. First, form errors of the nonrigid part are not fully captured in existing methods. Second, variation visualization can significantly enhance understanding of the geometric variation effects, but it is difficult to achieve under existing approaches. Inspired by the idea of a parametric space envelope, this article proposes a new methodology by building a variation tool to aid the task. Under the proposal, the geometric variation of the compliant part is indirectly modeled through the constructed variation tool. This indirect modeling enables capturing intrapart interactions that are the major source of the inaccuracy of existing methods. The simulated geometric variation can be visualized through the variation tool. In addition, the developed method does not rely on historical manufacturing experience. This can be valuable for early stage designer when such production information is not available or expensive to get. Furthermore, the proposed method can be integrated into existing computer-aided design (CAD), computer-aided manufacturing (CAM), and computer-aided engineering (CAE) systems to improve overall design quality and reduce reliance on multiple physical prototyping.

A Novel Model for the Tolerancing of Nonrigid Part Assemblies in Computer Aided Design

In the design step, the realistic modeling of the product represents an industrial requirement and a digital muck up (DMU) improvement. Thus, the tolerance integration in the computer aided design (CAD) model with the neglect of important physical factors, such as the components’ deformations during the mounting and assembly operation, causes a deviation between the numerical and the realistic models. In this regard, this paper presents a new model for the tolerance analysis of CAD assemblies based on the consideration of both manufacturing defects and deformations. The dimensional and geometrical tolerances are considered by the determination of assemblies’ configurations with defects based on the worst case tolerancing. The finite elements (FEs) simulation is realized with realistic models. An algorithm for updating the realistic mating constraints, between rigid and nonrigid parts, is developed. The case study of an assembly with planar and cylindrical joints is presented.

Suggestions of Define Methods by Rigid/Non-Rigid Parts’ Definitions

Defining and measuring non-rigid or flexible parts has been controversial in industry for many years. There are two primary areas of controversy. The first is agreeing on what exactly a non-rigid part is. The second is agreeing on how to define and measure a non-rigid part. The subject of non-rigid parts is further complicated by the brief coverage it receives in the national and international standards. This leaves each company to improvise or create its own rules for non-rigid parts. There are some who believe that Geometrical Dimensioning and Tolerancing (GD&T) should not be used on non-rigid parts. This is not true. The ASME Y14.5M standard applies to rigid parts as a default condition. However, there is no definition given for a rigid part. The term rigid part has been used in industry for so long that it has gained a definition by its general use. When most people in industry say rigid part, they are referring to a part doesn’t move (deform or flex) when a force (including gravity) is applied. How much force is relative based on the part characteristics. In reality, all parts will deform (or flex) if enough force is applied. Using this logic, all parts would be considered non-rigid. However, we all know that this is not how parts are treated in industry. Although GD&T defaults to rigid parts, it should also be used on non-rigid parts with a few special techniques. Actually 50~60% of all products designed contain parts or features on parts that are non-rigid. Therefore, we try to suggest the definitions of rigid and non-rigid parts and method to measure non-rigid parts.

Quantification of nonrigid liver deformation in radiofrequency ablation interventions using image registration

Multimodal image fusion for image guidance in minimally invasive liver interventions generally requires the registration of pre-operatively acquired images with interventional images of the patient. Whereas rigid registration approaches are fast and can be used in an interventional setting, the actual liver deformation may be nonrigid. The purpose of this paper is to assess the magnitude of nonrigid deformation of the liver between pre-operative and interventional CT images in the case of tumor ablations, over the full liver and over parts of the liver that match the volumes typically imaged by a 3D ultrasound transducer. We acquired 3D abdominal CT scans of 38 patients that had undergone the radiofrequency ablation of liver tumors, pre-operative CT images as well as intraoperative CT images. To determine the magnitude of liver deformation due to pose changes and respiration, we nonrigidly registered the pre-operative CT scan with the intraoperative CT scan. By fitting the deformation to a rigid transformation in the region of interest and computing the residual displacements, the nonrigid deformation part can be quantified. We performed quantifications over the complete liver, as well as for two volumes of interest representative of sub-xiphoidal and intercostal 3D ultrasound acquisitions. The results showed that a substantial amount of nonrigid deformation was found, and rotation of the patient’s pose and deep inhalation caused significant liver deformation. Hence we concluded that nonrigid motion correction in the interventions should be taken into account.

“What-if” scenarios towards virtual assembly-state mounting for non-rigid parts inspection using permissible loads

Recent developments in the fixtureless inspection of non-rigid parts based on computer-aided inspection (CAI) methods significantly contribute to diminishing the time and cost of geometrical dimensioning and inspection. Generally, CAI methods aim to compare scan meshes, which are acquired using scanners as point clouds from non-rigid manufactured parts in a free-state, with associated nominal computer-aided design (CAD) models. However, non-rigid parts are deformed in a free-state due to their compliance behavior. Industrial inspection approaches apply costly and complex physical inspection fixtures to retrieve the functional shape of non-rigid parts in assembly-state. Therefore, fixtureless inspection methods are developed to eliminate the need for these complex fixtures and to replace them with simple inspection supports. Fixtureless inspection methods intend to virtually (numerically) compensate for flexible deformation of non-rigid parts in a free-state. Inspired by industrial inspection techniques wherein weights (e.g., sandbags) are applied as restraining loads on non-rigid parts, we present a new fixtureless inspection method in this article. Our proposed virtual mounting assembly-state inspection (VMASI) method aims at predicting the functional shape (in assembly-state) of a deviated non-rigid part (including defects such as plastic deformation). This method is capable of virtually mounting the scan mesh of a deviated non-rigid part (acquired in a free-state) into the designed assembly-state. This is fulfilled by applying permissible restraining forces (loads) that are introduced as pressures on surfaces of a deviated part. The functional shape is then predicted via a linear FE-based transformation where the value and position of required restraining pressures are assessed by our developed restraining pressures optimization (RPO) approach. In fact, RPO minimizes the orientation difference and distance between assembly mounting holes on the predicted shape of a non-rigid part with respect to nominal ones on the CAD model. Eventually, the inspection is accomplished by examining the mounting holes offset on the predicted shape of the scan model concerning the nominal CAD model. This ensures that the mounting holes on the predicted shape of a scan model in assembly-state remain in the dedicated tolerance range. This method is evaluated on two non-rigid parts to predict the required restraining pressures limited to the permissible forces during the inspection process and to predict the eventual functional shape of the scan model. We applied numerical validations for each part, for which different types of synthetic (numerically simulated) defects are included into scan meshes, to determine whether the functional shape of a geometrically deviated part can be virtually retrieved under assembly constrains.

A robust and automated FE-based method for fixtureless dimensional metrology of non-rigid parts using an improved numerical inspection fixture

Dimensional inspection is an important element in the quality control of mechanical parts that have deviations from their nominal (CAD) model resulting from the manufacturing process. The focus of this research is on the profile inspection of non-rigid parts, which are broadly used in the aeronautic and automotive industries. In a free-state condition, due to residual stress and gravity loads, a non-rigid part can have a different shape compared with its assembled condition. To overcome this issue, specific inspection fixtures are usually allocated in industry to compensate for the displacement of such parts in order to simulate the use state and accomplish dimensional inspections. These dedicated fixtures, their installation and the inspection process consume a large amount of time and cost. Therefore, our principal objective has been to develop an inspection plan for eliminating the need for specialised fixtures by digitizing the displaced part’s surface using a contactless (optical) measuring device and comparing the acquired point cloud with the CAD model to identify deviations. In our previous work, we developed an approach to numerically inspect the profile of a non-rigid part using a non-rigid registration method and finite element analysis. To do so, a simulated displacement was performed using an improved definition of boundary conditions for simulating unfixed parts. In this paper, we will improve on the method and save time by increasing the accuracy of displacement boundary conditions and using automatic node insertion and finite element analysis. The repeatability and robustness of the approach will be also studied, and its metrological performance will be analysed. We will apply the improved method on two industrial non-rigid parts with free-form surfaces simulated with different types of displacement, defect and measurement noise (for evaluation of robustness).

Guideline for Fast Creating Virtual Mould of the Flat Feet

It is quite difficult to quickly design the special inserts or shoes for the particular patient who faces the problem about foot’s shape. Well-mould designing can make the geometric shapes of the inserts to be properly fitted to the feet, as the results, the pains can be relieved where the patient can perform the daily activities with more comfortable. To quickly copy near-net shape of the virtual model from the master part, the integrating between reverse engineering and slush casting has been applied where the Automated Selective Acquisition System (ASAS) has been applied in this research as the alternative reflective-scanning method to obtain an organized data set without applying any data reduction processes. For assisting the ASAS technique to quickly acquire the non-rigid part as feet, generating the solid feet by slush casting technique has been firstly performed where the various materials have been studied under the criteria of economical-based impression and non-skin allergic problems.

A Feature Learning and Object Recognition Framework for Underwater Fish Images.

Live fish recognition is one of the most crucial elements of fisheries survey applications where the vast amount of data is rapidly acquired. Different from general scenarios, challenges to underwater image recognition are posted by poor image quality, uncontrolled objects and environment, and difficulty in acquiring representative samples. In addition, most existing feature extraction techniques are hindered from automation due to involving human supervision. Toward this end, we propose an underwater fish recognition framework that consists of a fully unsupervised feature learning technique and an error-resilient classifier. Object parts are initialized based on saliency and relaxation labeling to match object parts correctly. A non-rigid part model is then learned based on fitness, separation, and discrimination criteria. For the classifier, an unsupervised clustering approach generates a binary class hierarchy, where each node is a classifier. To exploit information from ambiguous images, the notion of partial classification is introduced to assign coarse labels by optimizing the benefit of indecision made by the classifier. Experiments show that the proposed framework achieves high accuracy on both public and self-collected underwater fish images with high uncertainty and class imbalance.

3-D human pose recovery using nonrigid point set registration and body part tracking of depth data

In this paper, we present a novel approach for recovering a 3-D pose from a single human body depth silhouette using nonrigid point set registration and body part tracking. In our method, a human body depth silhouette is presented as a set of 3-D points and matched to another set of 3-D points using point correspondences. To recognize and maintain body part labels, we initialize the first set of points to corresponding human body parts, resulting in a body part-labeled map. Then, we transform the points to a sequential set of points based on point correspondences determined by nonrigid point set registration. After point registration, we utilize the information from tracked body part labels and registered points to create a human skeleton model. A 3-D human pose gets recovered by mapping joint information from the skeleton model to a 3-D synthetic human model. Quantitative and qualitative evaluation results on synthetic and real data show that complex human poses can be recovered more reliably with lower errors compared to other conventional techniques for 3-D pose recovery.

Fixtureless profile inspection of non-rigid parts using the numerical inspection fixture with improved definition of displacement boundary conditions

Quality control is an important factor for manufacturing companies looking to prosper in an era of globalization, market pressures, and technological advance. The functionality and product quality cannot be guaranteed without this important aspect. Manufactured parts have deviations from their nominal (CAD) shape caused by the manufacturing process. Thus, geometric inspection is a very important element in the quality control of mechanical parts. We have focused here on the profile inspection of non-rigid parts which are widely used in the aeronautic and automotive industries. Non-rigid parts can have different forms in a free-state condition compared with their nominal models due to residual stress and gravity loads. To solve this problem, dedicated inspection fixtures are generally used in industry to compensate for the displacement of such parts for simulating the use state in order to perform geometric inspections. These fixtures and the inspection process are expensive and time-consuming. Our aim is therefore to develop an inspection method which eliminates the need for specialized fixtures by acquiring a point cloud from the displaced part using a contactless measuring system such as optical scanning and comparing it with the CAD model for the identification of deviations. Using a non-rigid registration method and finite element analysis, we will numerically inspect the profile of a non-rigid part. To do so, a simulated displacement is performed using an improved definition of boundary conditions for simulating unfixed parts. In this paper, we will apply an improved method on two industrial non-rigid parts with free-form surfaces simulated with different types of displacement, defect, and measurement noise.

A virtual fixture using a FE-based transformation model embedded into a constrained optimization for the dimensional inspection of nonrigid parts

Virtually mounting nonrigid parts onto their fixture is proposed by researchers to remove the need for the use of complex physical inspection fixtures during the measurement process. Current approaches necessitate the pre-processing of the free-state nonrigid part’s point cloud into a suitable finite element (FE) mesh and are limited by the use of the boundary conditions setting methods available in FE software. In addition to these limits, these approaches do not take into account the forces used to restrain the part during the inspection, as commonly mandated for aerospace panels. To address these shortcomings, this paper presents a virtual fixture method that predicts the fixed shape of the part without the aforementioned drawbacks of current approaches. This is achieved by embedding information retrieved from a FE analysis of the nominal CAD model into a boundary displacement constrained optimization. To evaluate the proposed method, two case studies on physical parts are performed using the proposed virtual fixture method to evaluate the profile and assembly force specifications of each part.

To the question of definition of a deflection and pressing of non-rigid propeller shaft

The paper considers the impact of weight and cutting forces on deflection and pressing of the non-rigid part — propeller shaft. The analysis of literature sources in the field of kinematics and dynamics of the process of turning by the cup tools was conducted.The purpose of the work was stated as a result of the analysis. The purpose of this paper is to derive a mathematical expression of the dependence of deflection and pressing values of the non-rigid shaft on its own weight and cutting forces.The propeller shaft of the mine pump was selected as the object of research. The design of the propeller shaft is characterized as non-rigid. Therefore, it was the object of further researches.To derive the mathematical expression of shaft deflection under its own weight, the weight was considered as a uniformly distributed load.Differential equation of Euler-Bernoulli was used in order to solve this problem. In the process of turning, round tool under the influence of feed moves along the workpiece and presses on it in every particular point. The Vereshchagin’s method was used to derive the mathematical expression of shaft deflection from the cutting force.The results obtained in this work can be applied to the process of turning of all non-rigid shafts by the round cup tool.The mathematical expressions of deflection of the propeller shaft under its own weight and its pressing by the cutting forces allow optimizing the process of turning and improving the accuracy and quality of processing.