A framework for tolerance modeling based on parametric space envelope

Geometric dimensioning and tolerancing (GD&T) tolerance standards are widely used in industries across the world. A mathematical model to formulate tolerance specifications to enable comprehensive tolerance analysis is highly desirable but difficult to build. Existing methods have limited success on this with form and profile tolerance modeling as a known challenge. In this paper, we propose a novel tolerance modeling framework and methodology based upon parametric space envelope, a purposely built variation tool constructed from base parametric curve. Under proposal, geometric variation (deviation as well as deformation) is modeled and linked to envelope boundary control points’ movement. This indirect tolerance modeling brings various benefits. It is versatile and can handle full set of tolerances specified under GD&T standards including form, profile, and runout tolerance. The proposal can deal with complex manufacturing part and is capable of providing modeling accuracy required by many applications. The proposed approach has added advantage of facilitating integration of various computer-aided systems to meet emerging industry demands on tolerancing in a new era of digital manufacturing. The proposed methodology is illustrated and verified with an industrial case example on a two-part assembly

Modeling variation in multi-station compliant assembly using parametric space envelope

Non-rigid compliant parts are widely used in industries. One of the biggest challenges facing industries is geometric variation management of these compliant parts which can directly impact product quality and functionality. Existing rigid body-based variation modeling approaches are not suitable for compliant assembly while finite element analysis based methods have the disadvantage of requiring heavy computation efforts and detailed design information which is unavailable during preliminary design phase. Hence, this paper develops a novel methodology to evaluate geometric variation propagation in multi-station compliant assembly based on parametric space envelope (i.e. variation tool constructed from parametric curves). Three sources of variation: location-led positional variation, assembly deformation-induced variation and station transition caused variation are analyzed. In this study, geometric variations are modeled indirectly through a compact set of boundary control points. Compared with existing methods where geometric variation is modeled by tracking key feature points on the manufacturing part, the proposed approach brings many benefits. It can handle arbitrary complex compliant part, and it lowers computation requirement in many real applications. The method is illustrated and verified through an industrial case study on a multi-station compliant panel assembly. The developed method provides industries a new way to manage geometric variation from compliant assembly

Error-Bounded and Feature Preserving Surface Remeshing with Minimal Angle Improvement

The typical goal of surface remeshing consists in finding a mesh that is (1) geometrically faithful to the original geometry, (2) as coarse as possible to obtain a low-complexity representation and (3) free of bad elements that would hamper the desired application. In this paper, we design an algorithm to address all three optimization goals simultaneously. The user specifies desired bounds on approximation error {\delta}, minimal interior angle {\theta} and maximum mesh complexity N (number of vertices). Since such a desired mesh might not even exist, our optimization framework treats only the approximation error bound {\delta} as a hard constraint and the other two criteria as optimization goals. More specifically, we iteratively perform carefully prioritized local operators, whenever they do not violate the approximation error bound and improve the mesh otherwise. In this way our optimization framework greedily searches for the coarsest mesh with minimal interior angle above {\theta} and approximation error bounded by {\delta}. Fast runtime is enabled by a local approximation error estimation, while implicit feature preservation is obtained by specifically designed vertex relocation operators. Experiments show that our approach delivers high-quality meshes with implicitly preserved features and better balances between geometric fidelity, mesh complexity and element quality than the state-of-the-art.Comment: 14 pages, 20 figures. Submitted to IEEE Transactions on Visualization and Computer Graphic

Design exploration through bidirectional modeling of constraints

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Architecture, 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 315-324).Today digital models for design exploration are not used to their full potential. The research efforts in the past decades have placed geometric design representations firmly at the center of digital design environments. In this thesis it is argued that models for design exploration that bridge different representation aid in the discovery of novel designs. Replacing commonly used analytical, uni-directional models for linking representations, with bidirectional ones, further supports design exploration. The key benefit of bidirectional models is the ability to swap the role of driver and driven in the exploration. The thesis developed around a set of design experiments that tested the integration of bidirectional computational models in domain specific designs. From the experiments three main exploration types emerged. They are: branching explorations for establishing constraints for an undefined design problem; illustrated in the design of a concept car. Circular explorations for the refinement of constraint relationships; illustrated in the design of a chair. Parallel explorations for exercising well-understood constraints; illustrated in a form finding model in architecture. A key contribution of the thesis is the novel use of constraint diagrams developed to construct design explorers for the experiments. The diagrams show the importance of translations between design representations in establishing design drivers from the set of constraints. The incomplete mapping of design features across different representations requires the redescription of the design for each translation.(cont.) This redescription is a key aspect of exploration and supports design innovation. Finally, this thesis argues that the development of design specific design explorers favors a shift in software design away from monolithic, integrated software environments and towards open software platforms that support user development.by Axel Kilian.Ph.D

Volumetric Data Analysis for Reverse Engineering and Solid Additive Manufacturing: A Framework for Geometric Metrological Analysis

Poor geometric quality is one of the main constraints that hinders the wide adoption of reverse engineering (RE) and additive manufacturing (AM). RE models from a single scan will most likely generate inaccurate representations of the original design due to the uncertainties existing in individual parts and scanning procedures. On the other hand, metrological methodologies for AM significantly differ from those for the traditional manufacturing processes. Conventional statistical methodologies overlook these three-dimensional (3D) feature-independent processing techniques. In this dissertation, we develop a novel statistical data analysis framework---volumetric data analysis (VDA)---to deal with the uniqueness of both technologies. In general, this framework also addresses the rising analytical needs of 3D geometric data. Through VDA, we can simultaneously analyze the measured points on the outer surfaces and their relationships to acquire manufacturing knowledge. The main goal of this dissertation is to apply the proposed framework in multiple RE and AM applications related to their geometric quality characteristics. First, we demonstrate a novel estimator to increase the precision of RE-generated models. We built a Bayesian model with prior domain knowledge to model the landmarks’ uncertainty. We also proposed a bi-objective optimization model to answer the RE process-planning questions, e.g., how many scans and parts are required to achieve the precision requirements. The second major contribution is a study of tolerance estimation procedure for the re-manufacturing of legacy parts. We propose a systematic geometric inspection methodology for the RE and AM systems. Moreover, based on the domain knowledge in production-process design and planning, we developed methods to estimate empirical tolerances from a small batch of legacy parts. The third major contribution of this dissertation is to design an automated variance modeling algorithm for 3D scanners. The algorithm utilizes a physical object’s local geometric descriptors and Bayesian extreme learning machines to predict the landmarks’ variances. Lastly, we introduce the VDA framework to AM-oriented experimental analysis. Specifically, we propose a high-dimensional hypothesis testing procedure to statistically compare the geometric production accuracy under two AM process settings. We present new visualization tools for deviation diagnostics to aid in interpreting and comparing the process outputs

Computational Techniques to Predict Orthopaedic Implant Alignment and Fit in Bone

Among the broad palette of surgical techniques employed in the current orthopaedic practice, joint replacement represents one of the most difficult and costliest surgical procedures. While numerous recent advances suggest that computer assistance can dramatically improve the precision and long term outcomes of joint arthroplasty even in the hands of experienced surgeons, many of the joint replacement protocols continue to rely almost exclusively on an empirical basis that often entail a succession of trial and error maneuvers that can only be performed intraoperatively. Although the surgeon is generally unable to accurately and reliably predict a priori what the final malalignment will be or even what implant size should be used for a certain patient, the overarching goal of all arthroplastic procedures is to ensure that an appropriate match exists between the native and prosthetic axes of the articulation. To address this relative lack of knowledge, the main objective of this thesis was to develop a comprehensive library of numerical techniques capable to: 1) accurately reconstruct the outer and inner geometry of the bone to be implanted; 2) determine the location of the native articular axis to be replicated by the implant; 3) assess the insertability of a certain implant within the endosteal canal of the bone to be implanted; 4) propose customized implant geometries capable to ensure minimal malalignments between native and prosthetic axes. The accuracy of the developed algorithms was validated through comparisons performed against conventional methods involving either contact-acquired data or navigated implantation approaches, while various customized implant designs proposed were tested with an original numerical implantation method. It is anticipated that the proposed computer-based approaches will eliminate or at least diminish the need for undesirable trial and error implantation procedures in a sense that present error-prone intraoperative implant insertion decisions will be at least augmented if not even replaced by optimal computer-based solutions to offer reliable virtual “previews” of the future surgical procedure. While the entire thesis is focused on the elbow as the most challenging joint replacement surgery, many of the developed approaches are equally applicable to other upper or lower limb articulations

Geometric robustness and dynamic response management by structural topometry optimisation to reduce the risk for squeak and rattle

Historically, squeak and rattle (S&R) sounds have been among the top quality problems and a major contributor to the warranty costs in passenger cars. Geometric variation is among the main causes of S&R. Though, geometric variation analysis and robust design techniques have been passively involved in the open-loop design activities in the predesign-freeze phases of car development. Despite the successful application of topometry optimisation to enhance attributes such as weight, durability, noise and vibration and crashworthiness in passenger cars, the implementation of closed-loop structural optimisation in the robust design context to reduce the risk for S&R has been limited. In this respect, the main obstacles have been the demanding computational resources and the absence of quantified S&R risk evaluation methods. In this work, a topometry optimisation approach is proposed to involve the geometric variation analysis in an attribute balancing problem together with the dynamic response of the system. The proposed method was used to identify the potential areas of a door component that needed structural reinforcement. The main objective was to enhance the design robustness to minimise the risk for S&R by improving the system response to static geometrical uncertainties and dynamic excitation

Rethinking of timber joinery in 21st-century architecture The computation of a timber joinery through complex geometry

Master of ScienceDepartment of ArchitectureMajor Professor Not ListedIn recent years, there has been a renewed interest in timber joinery in contemporary architecture. With the introduction of digital fabrication technologies and computational design, it is now possible to create complex timber structures with more complex shapes and designs. One of the critical advantages of timber as a building material is its ability to be combined in various ways. Timber joinery can create solid and durable connections between structural members while providing an aesthetically pleasing finish. In the 21st century, architects and designers are exploring new ways to use timber joinery to create unique and innovative structures. Computational design tools allow designers to create complex geometries that can be fabricated precisely using computer numerical control (CNC) machines and other digital fabrication technologies. Designers who are well-versed in programs like Rhino, Grasshopper, or Revit have the ability to utilize parametric modeling software that can calculate timber joinery that is based on intricate geometry. These tools allow designers to create 3D models of the structure and conduct experiments with different joinery options and configurations. Once the joinery is designed, it can be fabricated using CNC machines or other digital fabrication tools. It allows for high precision and accuracy in the fabrication process, ensuring the joint perfectly fits together. The use of complex timber joinery in contemporary architecture provides functional benefits and a unique aesthetic that cannot be achieved with other materials. By rethinking traditional joinery techniques and embracing digital technologies, architects and designers can create structures that push the boundaries of what is possible through timber construction. This thesis will investigate and explore the timber joinery system and fabrication methods, one of the old wooden structure techniques used in the age of digital technologies that rejuvenate the usage of conventional construction processes in timber buildings. The main aim of this thesis was to study computational design in creating complex wooden segmental base structures that rely on interlocking timber joints as the primary form of connection. This involved analyzing the role of wooden joinery and exploring complex systems made using this technique. The second objective was to create a digital model of several types of parametric wood joineries, such as halve and lap joint, Tenon and mortise joint, and finger joints. A digital model of a complex segmental plate structure with three fundamental parametric joints was also developed. The three basic types include finger, halve and lap clip, and Mortise and Tenon joints. The third objective is a structural and shape optimization of the basic mesh for specified complex geometry, which will be a digital model to evaluate the applicability of the generated joints, and will be determined because of this investigation

Large Deformable Soft Actuators Using Dielectric Elastomer and Origami Inspired Structures

There have been significant developments in the field of robotics. Significant development consists of new configurations, control mechanisms, and actuators based upon its applications. Despite significant improvements in modern robotics, the biologically inspired robots has taken the center stage. Inspired by nature, biologically inspired robots are called ‘soft robots’. Within these robots lies a secret ingredient: the actuator. Soft robotic development has been driven by the idea of developing actuators that are like human muscle and are known as ‘artificial muscle’. Among different materials suitable for the development of artificial muscle, the dielectric elastomer actuator (DEA) is capable of large deformation by applying an electric field. Theoretical formulation for DEA was performed based upon the constitutive hyperelastic models and was validated by using finite element method (FEM) using ABAQUS. For FEM, multistep analysis was performed to apply pre-stretch to the membrane before applying actuation voltage. Based on the validation of DEA, different configurations of DEA were investigated. Helical dielectric elastomer actuator and origami dielectric elastomer actuator were investigated using theoretical modeling. Comparisons were made with FEM to validate the model. This study focus on the theoretical and FEM analysis of strain within the different configuration of DEA and how the actuation strain of the dielectric elastomer can be translated into contraction and/or bending of the actuator