Combined 3D thinning and greedy algorithm to approximate realistic particles with corrected mechanical properties

The shape of irregular particles has significant influence on micro- and macro-scopic behavior of granular systems. This paper presents a combined 3D thinning and greedy set-covering algorithm to approximate realistic particles with a clump of overlapping spheres for discrete element method (DEM) simulations. First, the particle medial surface (or surface skeleton), from which all candidate (maximal inscribed) spheres can be generated, is computed by the topological 3D thinning. Then, the clump generation procedure is converted into a greedy set-covering (SCP) problem. To correct the mass distribution due to highly overlapped spheres inside the clump, linear programming (LP) is used to adjust the density of each component sphere, such that the aggregate properties mass, center of mass and inertia tensor are identical or close enough to the prototypical particle. In order to find the optimal approximation accuracy (volume coverage: ratio of clump's volume to the original particle's volume), particle flow of 3 different shapes in a rotating drum are conducted. It was observed that the dynamic angle of repose starts to converge for all particle shapes at 85% volume coverage (spheres per clump < 30), which implies the possible optimal resolution to capture the mechanical behavior of the system.Comment: 34 pages, 13 figure

A novel haptic model and environment for maxillofacial surgical operation planning and manipulation

This paper presents a practical method and a new haptic model to support manipulations of bones and their segments during the planning of a surgical operation in a virtual environment using a haptic interface. To perform an effective dental surgery it is important to have all the operation related information of the patient available beforehand in order to plan the operation and avoid any complications. A haptic interface with a virtual and accurate patient model to support the planning of bone cuts is therefore critical, useful and necessary for the surgeons. The system proposed uses DICOM images taken from a digital tomography scanner and creates a mesh model of the filtered skull, from which the jaw bone can be isolated for further use. A novel solution for cutting the bones has been developed and it uses the haptic tool to determine and define the bone-cutting plane in the bone, and this new approach creates three new meshes of the original model. Using this approach the computational power is optimized and a real time feedback can be achieved during all bone manipulations. During the movement of the mesh cutting, a novel friction profile is predefined in the haptical system to simulate the force feedback feel of different densities in the bone

Virtual reality for assembly methods prototyping: a review

Assembly planning and evaluation is an important component of the product design process in which details about how parts of a new product will be put together are formalized. A well designed assembly process should take into account various factors such as optimum assembly time and sequence, tooling and fixture requirements, ergonomics, operator safety, and accessibility, among others. Existing computer-based tools to support virtual assembly either concentrate solely on representation of the geometry of parts and fixtures and evaluation of clearances and tolerances or use simulated human mannequins to approximate human interaction in the assembly process. Virtual reality technology has the potential to support integration of natural human motions into the computer aided assembly planning environment (Ritchie et al. in Proc I MECH E Part B J Eng 213(5):461–474, 1999). This would allow evaluations of an assembler’s ability to manipulate and assemble parts and result in reduced time and cost for product design. This paper provides a review of the research in virtual assembly and categorizes the different approaches. Finally, critical requirements and directions for future research are presented

The application of three-dimensional mass-spring structures in the real-time simulation of sheet materials for computer generated imagery

Despite the resources devoted to computer graphics technology over the last 40 years, there is still a need to increase the realism with which flexible materials are simulated. However, to date reported methods are restricted in their application by their use of two-dimensional structures and implicit integration methods that lend themselves to modelling cloth-like sheets but not stiffer, thicker materials in which bending moments play a significant role. This thesis presents a real-time, computationally efficient environment for simulations of sheet materials. The approach described differs from other techniques principally through its novel use of multilayer sheet structures. In addition to more accurately modelling bending moment effects, it also allows the effects of increased temperature within the environment to be simulated. Limitations of this approach include the increased difficulties of calibrating a realistic and stable simulation compared to implicit based methods. A series of experiments are conducted to establish the effectiveness of the technique, evaluating the suitability of different integration methods, sheet structures, and simulation parameters, before conducting a Human Computer Interaction (HCI) based evaluation to establish the effectiveness with which the technique can produce credible simulations. These results are also compared against a system that utilises an established method for sheet simulation and a hybrid solution that combines the use of 3D (i.e. multilayer) lattice structures with the recognised sheet simulation approach. The results suggest that the use of a three-dimensional structure does provide a level of enhanced realism when simulating stiff laminar materials although the best overall results were achieved through the use of the hybrid model

Mekaanisen kokoonpanon harjoitteluun tarkoitetun virtuaalitodellisuuteen perustuvan ohjelman suunnittelu ja toteutus

Although virtual assembly has been studied for over 20 years, it has not yet reached a state where it would enjoy widespread usage outside of academia despite the possible cost savings and improvements in the effectiveness of the training. Even though there have been multiple separate studies on virtual assembly, hand-based interaction, and assembly assistance, we have not found applications that would combine all of these to provide a complete assembly training experience. The goal of this thesis was to design and implement a virtual reality application for mechanical assembly training. In our application, we provide a natural user interaction by using a Leap Motion controller, a hand tracking device mounted onto a virtual reality headset. The application was implemented using the Unity game engine and supports both Oculus and SteamVR compatible VR headsets. Unlike most of the previous systems, we combine the use of hand-based interaction, assembly simulation, and context-aware assembly guidance to create an all-in-one VR assembly solution. As a part of our implementation, we propose a new method for assembly guidance and validation that works by matching assemblies built by the user to the assembly the user is supposed to build. Based on the user testing results, there is an interest in this kind of application. Although the inaccuracies with the hand and finger tracking hindered the usability of the application, the users described the application as surprisingly easy to use once they learned how to overcome these issues.Siitä huolimatta, että virtuaalista kokoonpanoa on tutkittu yli 20 vuotta, ja se voisi tarjota sekä kustannussäästöjä että jopa parantaa harjoittelun tehokkuutta, se ei ole vielä saavuttanut vakiintunutta asemaa akateemisen tutkimuksen ulkopuolella. Vaikka virtuaalisesta kokoonpanosta, käsipohjaisesta vuorovaikutuksesta ja kokoonpanon avustamisesta on tehty useita erillisiä tutkimuksia, emme ole löytäneet sovelluksia, jotka yhdistäisivät kaikki nämä kokonaisvaltaisen harjoitusalustan tarjoamiseksi. Tämän diplomityön tarkoituksena oli suunnitella ja toteuttaa virtuaalitodellisuuteen perustuva työkalu mekaanisen kokoonpanon harjoitteluun. Ohjelmamme tarjoaa luonnollisen, käsien seurantaan perustuvan käyttöliittymän hyödyntämällä virtuaalilaseihin kiinnitettyä Leap Motion -ohjainta. Sovellus toteutettiin käyttäen Unity-pelimoottoria ja sovellus tukee sekä Oculus- että SteamVR-yhteensopivia virtuaalitodellisuuslaseja. Toisin kuin useimmat vastaavat järjestelmät, meidän työkalumme yhdistää käsin tapahtuvan interaktion, kokoonpanosimulaation ja kontekstisidonnaiset kokoonpano-ohjeet tarjoten kokonaisvaltaisen sovelluksen virtuaalisen kokoonpanon harjoitteluun. Osana työkaluamme kehitimme uuden menetelmän kokoonpanon aikana tapahtuvien virheiden havainnoimiseen ja kontekstisidonnaisten kokoamisohjeiden muodostamiseen. Kehittämämme menetelmä perustuu vastaavuuksien etsimiseen käyttäjän kokoamien tuotteiden ja tavoitteena olevan tuotteen väliltä. Käyttäjätestauksesta saatujen tulosten perusteella tämänkaltaiselle sovellukselle olisi kysyntää. Vaikka käsienseurantalaitteen epätarkkuus haittasi sovelluksen käytettävyyttä, käyttäjät luonnehtivat sovellusta yllättävän helppokäyttöiseksi opittuaan työskentelemään sovelluksen parissa