| The essential function of a mechanical assembly is the removal of degrees of freedom (DOF) and transfer of load between two bodies. Assemblies using integral attachments are composed of unilateral mating surfaces, where quality is greatly affected by the location and orientation of assembly features. Feature-level design is concerned with the dimension, stress, and strain of individual assembly features. This dissertation is concerned with attachment-level design, where design decisions are made on the type, location, and orientation of assembly features.;Previous research in theoretical kinematics, robotic grasping, and fixture design have produced either a binary test for form closure or design optimization for a specific loading condition. There is currently no tool available to: (1) analyze an assembly's quality with a quantitative metric and (2) optimize the design of the assembly constraint configuration (location and orientation of features) to resist motion effectively. Therefore, the objective of this dissertation is to develop an analysis and design tool to address these needs.;The analysis tool models the assembly features as wrench systems. The point, pin, line, and plane constraints in assembly are modeled with equivalent first, second, and third order wrench systems. The methodology used is based on composing a five-system pivot wrench combination to which a screw motion is reciprocal. The resistance effectiveness of each constraint to these motions is calculated as the ratio of the reaction forces at each resisting constraint to the input wrench magnitude. Based on these individual resistance values, a set of rating metrics is calculated to evaluate an assembly's quality from different perspectives. A design tool based on this analysis methodology is developed to optimize assembly design by constraint modification, constraint reduction, and constraint addition. A set of case studies is used to verify commonly known design principles, explore the design space of attachment, and understand trade-offs in assembly constraint redundancy and resistance quality.;The main contributions of this dissertation are: (1) an analysis tool that is able to model assembly as kinematic constraints and calculate the load amplification ratio in the form of different rating metrics to measure assembly quality, (2) a design tool that is able to explore the design space and find optimal solutions for improving constraint effectiveness and optimize the number of constraints, and (3) an understanding of how constraint modification, reduction, and addition affect the quality of an assembly. |
