Title page for ETD etd-091899-163323

Type of Document Master's Thesis
Author Marehalli, Jayavardhan N
URN etd-091899-163323
Title Assembly Sequence Optimization and Assembly Path Planning
Degree Master of Science
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
Sturges, Robert H. Committee Chair
Deisenroth, Michael P. Committee Member
Myklebust, Arvid Committee Member
Reinholtz, Charles F. Committee Member
  • Liaison diagram
  • principal contacts
  • constraints
  • index of difficulty
Date of Defense 1999-08-31
Availability restricted
This thesis addresses two important aspects of automatic assembly viz., assembly

sequence planning and assembly path planning. These issues are addressed separately

starting with sequence planning followed by assembly path planning.

For efficient assembly without feedback systems (or, passive assembly), an assembler

should know the ideal orientation of each component and the order in which to put the parts

together (or, assembly sequence). A heuristic is presented to find the optimal assembly

sequence and prescribe the orientation of the components for a minimum set of grippers =

ideally one. The heuristic utilizes an index of difficulty (ID) that quantifies assembly. The

ID for each task in the assembly process is computed on the basis of a number of geometrical

and operational properties. The objective of the optimization problem here is to minimize the

assembly ID and categorize parts/subassemblies based on their preferred direction of

assembly while allowing re-orientation of the base part. It is assumed that the preferred

direction of assembly is vertically downward, consistent with manual as well as most

automatic assembly protocols. Our attempt is to minimize the number of degrees of freedom

required in a re-orienting fixture and derive the requirements for such a fixture. The assembly of a small engine is used as an example in this study due to the variety of ideally

rigid parts involved.

In high precision assembly tasks, contact motion is common and often desirable. This

entails a careful study of contact states of the parts being assembled. Recognition of contact

states is crucial in planning and executing contact motion plans due to inevitable

uncertainties. Dr. Jing Xiao of UNCC introduced the concept of principal contacts (PC) and

contact formation (CF) for contact state recognition. The concept of using CFs (as sets of

PCs) has the inherent advantage that a change of CF is often coincident with a discontinuity

of the general contact force (force and torque). Previous work in contact motion planning

has shown that contact information at the level of PCs along with the sensed location and

force information is often sufficient for planning high precision assembly operations. In this thesis, we present results from experiments involving planned contact motions to validate the

notion of PCs and CFs -- an abrupt change in general contact force often accompanies a

change between CFs. We are only concerned with solving the 2D peg-in-corner problem.

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[VT] COVER_PAGE.PDF 143.01 Kb 00:00:39 00:00:20 00:00:17 00:00:08 < 00:00:01
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