Computational Analysis and Design of Structurally Stable Assemblies with Rigid Parts

An assembly refers to a collection of parts joined together to achieve a specific form and/or functionality. Assemblies make it possible to fabricate large and complex objects with several small and simple parts. Such parts can be assembled and disassembled repeatedly, benefiting the transportation and maintenance of the assembly. Due to these advantages, assemblies are ubiquitous in our daily lives, including most furniture, household appliances, and architecture. The recent advancement in digital fabrication lowers the hurdles for fabricating objects with complex shapes. However, designing physically plausible assemblies is still a non-trivial task as a slight local modification on a part's geometry could have a global impact on the structural and/or functional performance of the whole assembly. New computational tools are developed to enable general users involved in the design process exploiting their imagination. This thesis focuses on static assemblies with rigid parts. We develop computational methods for analyzing and designing assemblies that are structurally stable and assemblable. To address this problem, we use integral joints i.e., tenon and mortise, that are historically used because of their reversibility which simplifies the disassembly process significantly. Properly arranged integral joints can restrict parts' relative movement for improved structural stability. However, manually finding the right joints' geometry is a tedious and error-prone task. Inspired by the kinematic-static duality, we first propose a new kinematic-based method for analyzing the structural stability of assemblies. We then develop a two-stage computational design framework based on this new analyzing method. The kinematic design stage determines the amount of motion restrictions imposed by joints to make a given assembly stable in the motion space. The geometric design stage searches for proper shapes of the joints to satisfy the motion restriction requirements computed from the previous stage. To solve the problem numerically, we propose the joint motion cones to measure the motion restriction capacity of given joints. Compared with previous works, our framework can efficiently handle inputs with complex geometry. Besides, our design framework is very flexible and can easily be adapted to various applications:First, we focus on designing globally interlocking assemblies that can withstand arbitrary external forces and torques. Second, we are interested in designing assemblies of rigid convex blocks to approximate freeform surfaces. Our design framework can optimize the blocks' shape to generate assemblies with good resistance against lateral forces, and in some cases, globally interlocking assemblies.Lastly, we present a method for designing complex assemblies with cone joints. By optimizing the shapes of cone joints, our design framework can find the best trade-off between structural stability and assemblability.We validate our computational tools by fabricating a series of physical prototypes. Our algorithms have great potential to be applied for solving various assembly design problems ranging from small-scale such as toys and furniture to large-scale such as art installation and architecture. For example, the proposed techniques could be applied for designing discrete architecture that can be automatically constructed with robots.

Iterative geometric design for architecture

Ivo Stotz

This work investigates on computer aided integrated architectural design and production. The aim is to provide integral solutions for the design and the production of geometrically complex free-form architecture. Investigations on computer aided geometric design and integrated manufacturing are carried out with equal importance. This research is considering an integral and interdisciplinary approach, including computer science, mathematics and architecture. Inspired by fractal geometry, the IFS formalism is studied with regards to discrete architectural geometric design. The geometric design method studied provides new shape control possibilities unifying two separate design paradigms of rough and smooth objects. Capable to design fractal geometric figures, the method also covers the generation of classical objects such as conics and NURBS-curves. Close attention has been paid to the design of iterative free-form surfaces, which are composed entirely out of planar elements. A surface method based on projected vector sums is proposed. The resulting geometric figures are expressed in a discrete form and can be easily translated into a coherent set of constructional elements. The studies for translation of the geometrical elements into constructional elements consider integrated manufacturing. Addressing and numbering of the elements by iterative geometric design are investigated and compared to lexicographically ordered addressing systems, in order to provide an adequate data structure for the design, production and assembly of the constructional elements. For the generation of the data describing constructional elements, problems related to thickening and offset meshes are discussed. Once the global geometry of the constructional part has been computed, parameters are defined for generic automated detailing. Hereby the entire description of the constructional elements is completed. These elements are mapped and packed with regards to the coordinate system of a CNC-machine and the properties and the dimensions of the raw material, providing the complete set of workshop plans needed for integrated manufacturing. For automated generation of machine instructions (G-code), machining strategies – depending on the type of machine used, tool and material properties – are elaborated. Finally, the integrated digital design methods studied within the scope of this thesis are tested and verified by the realization of different reduced scale prototypes. The studied applications range from bearing vault structures to fractal and smooth timber panel shell structures. The developed methods have shown to be efficient for the design and the realization of geometrically complex architectural objects. The required planning effort to handle and manipulate the design and the production data has been greatly reduced. Some of the proposed methods have proved to be robust and general enough to be applied on real world applications. Iterative geometric design provides high degree of design possibilities offering an efficient tool for the creation of smooth and rough free form objects. The possibility to incorporate successive folds in free-form objects allows structural applications.

EPFL2009

Space, people, networks

Selena Savic

In this thesis, I investigate wireless communication from an architectural perspective. I am using design prototypes to explore possibilities for interaction and designing with wirelessness in mind. The public primarily regards wireless networking technology as a technical infrastructure that should provide a seamless flow of information across a network of base stations, access points and mobile devices. From this perspective, wireless infrastructure is evaluated in terms of network availability and speed, and is continuously optimised. Researchers explored some other perspectives on wireless communication technology: they used computational spatial analysis to measure signal propagation in space. Some ethnographic studies explored its effect on the use of public space. Wireless connectivity was also explored through the philosophical framework of radical empiricism. All this points to the fact that wireless network infrastructure is a complex topic, spanning multiple fields of expertise and interest (engineering, architecture, urban studies but also sociology and philosophy). It is rarely explored from a plural perspective, as each study typically focuses on the one aspect within its expertise. I propose a more complex view of wireless connectivity, encompassing these different perspectives through an intellectual framework that is based on the notion of architecturality. Architecturality, a property common to all architecture but exceeding the limits of built artefacts, is a measure of the effect something has on the experience of space. Through the lens of the built environment, I expose the complex transactions that take place between networks, people and space. In order to evaluate architecturality of wireless communication signals, I conducted a series of practical design experiments, involving people and interactive installations, and using data gathered from mobile devices and wireless access points. The design of these experiments relies on the principles described by human-computer interaction (HCI) researchers as seamful design. Seamful design reveals underlying structures and relationships behind what appears as a utilitarian infrastructure. The design experiments contribute to the discussion on the use of design artefacts in practice-based research methodologies, thus challenging the different agents of knowledge production and the superiority of established research traditions. The insights gained from this complex examination of wireless networks are important for architectural design, as a way to account more adequately for signal propagation through buildings. The experience of internalising wireless networks in the process of design engenders a designerâs sensitivity towards the presence of wireless communications in space. This sensitivity, similar to the one we have for the distribution of natural and artificial lighting, will be needed in the ever more challenging design of the built environment. The sensible designer can account for, and envision, more dynamic environments that are able to accommodate change and information in completely new ways.

EPFL2015

Méthode systématique de conception de cinématiques parallèles

Parallel kinematics structures currently find increasing industrial applications, particularly in packaging and assembly. With very few exceptions, machine-tools with parallel kinematics are limited to mechanisms with three or six degrees of freedom. Moreover, the spindle tilt is limited to very small angles. The advantages of parallel kinematics structures are high precision, lower fabrication cost, good dynamics and high stiffness. This dissertation proposes a systematic configuration design method for the development of new parallel kinematics structures. The parallel structures obtained with this method combine large spindle tilt angles with the advantages of parallel kinematics structures. First, components and characteristic elements of parallel structures are defined and the description of a proposed systematic method for configuration design, the "Design Cube Method", follows. The method enables the design of a family of parallel structures with a specified number and arrangement of mobilities. Methods such as "Gruebler's Formula" and the "Method of Intersecting Trajectories" serve to quickly verify the desired number of degrees of freedom of the structure and the optimal arrangement of the kinematic chains. Several mechanisms are described, that once integrated in a parallel structure, significantly increase the range of tilt of the end-effector, while keeping the stiffness as constant and as high as possible. A new parallel kinematics structure for a five-axis machine-tool has been developed using the new design methods described above. The performance specifications are listed, the desired arrangement of the axis is described and the design cube method is used to generate a new family of parallel kinematics structures. The various structures are evaluated in terms of how suited they are for machine-tool applications, and of the ease of integration of a mechanism to improve the tilt of the end-effector. A laboratory mock-up, demonstrating the various principles, and an industrial prototype of the new machine, the Hita-PDR, have been developed and fabricated. The bar lengths of the structure were selected so as to avoid singularities of the structure in the desired workspace. The specified high stiffness of the industrial prototype required the development of a new type of joint, the simple and double spherical joints with line contact. The high performances of the industrial prototype confirm the machine concept and the relevant choice of the parallel kinematics structure. This dissertation gives a global vision, of the various stages in the design of parallel kinematics structures with large rotations of the end-effector and high stiffness, starting with initial specifications, all the way up to the detailed design and manufacturing of the machine.

EPFL2004