Optimization of Constraint Location, Orientation, and Quantity in Mechanical Assembly

Abstract

A mechanical assembly aims to remove 6 degree-of-freedom (DOF) motion between two or more parts using features such as fasteners, integral attachments, and mating surfaces, all of which act as constraints. The locations, orientations, and quantity of these constraints directly influence the effectiveness of a constraint configuration to eliminate DOF; therefore, constraint design decisions are crucial to the performance of a mechanical assembly. The design tool presented in this paper uses an analysis tool developed by the authors to explore a user-specified constraint design space and help the designer make informed decisions based on quantitative data so as to optimize constraint locations and orientations. The utility of the design tool is demonstrated with an assembly case study that contains both threaded fasteners and integral attachments. The results identify the opportunity for significant improvements by separately exploring individual design spaces associated with some constraints and further gains through a search of a multidimensional design space that leverages interaction effects between the location and orientation variables. The example also highlights how the tool can help identify nonintuitive solutions such as nonrectilinear, nonplanar parting lines. A trade-off study demonstrates how the design tool can quantitatively aid in optimizing the total number of constraints. Adding constraints generally improves an assembly's performance at the expense of increased redundancy, which can cause locked-in stresses and assembly inaccuracies, so the design tools helps identify new/removable constraints that offer the greatest/least contribution to the overall part constraint configuration. Through these capabilities, this design tool provides useful data to optimize and understand mechanical assembly performance variables.

Generating disassembly tasks for selective disassembly using ontology-based disassembly knowledge representation

“…Tseng et al (2004) classified fasteners to fixed fasteners and movable fasteners. Rusli et al (2013) pointed out that assembly is the removal of degree-of-freedom (DOF). For plastic components, DOF removal is accomplished through combinations of mating surfaces, threaded fasteners and snap-fits.…”

Recognition of Kinematic Joints of 3D Assembly Models Based on Reciprocal Screw Theory

“…References [23][24][25] analyzed the state of a constraint of an assembly, mechanism, or fixture to see if it is properly constrained or whether it contains unwanted overconstraints. Rusli et al [26,27] addressed attachment-level design, in which decisions are made to establish the types, locations, and orientations of assembly features. Su et al [28] analyzed the mobility of overconstrained linkages and compliant mechanisms.…”

“…According to , if the screw representations between any two parts of the assembly model are known, we can easily analyze the model's kinematic functions. References [4][5][6][7][8][9][10][11][12][13][23][24][25][26][27][28][29] manually model the corresponding screw system. Thus, it is time consuming when the machine is large and complex.…”