Haptic-assisted virtual assembly and prototyping has seen significant attention over the past two decades. However, in spite of the appealing prospects, its adoption has been slower than expected. We identify the main roadblocks as the inherent geometric complexities faced when assembling objects of arbitrary shape, and the computation time limitation imposed by the notorious 1 kHz haptic refresh rate. We addressed the first problem in a recent work by introducing a generic energy model for geometric guidance and constraints between features of arbitrary shape. In the present work, we address the second challenge by leveraging Fourier transforms to compute the constraint forces and torques. Our new concept of “geometric energy” field is computed automatically from a cross-correlation of “skelet al densities” in the frequency domain, and serves as a generalization of the manually specified virtual fixtures or heuristically identified mating constraints proposed in the literature. The formulation of the energy field as a convolution enables efficient computation using fast Fourier transforms (FFTs) on the graphics processing unit (GPU). We show that our method is effective for low-clearance assembly of objects of arbitrary geometric and syntactic complexity.
Up until recently, the two-phase framework has been widely accepted as the only promising future direction for performing haptic assembly tasks effectively @cite_2 . Among the main difficulties with this hybrid paradigm are detecting the proximity to an insertion site, properly switching between the two phases (i.e., blending' algorithms to turn CD off and activate constraint management @cite_49 ), and handling collision events outside the insertion site when CD is switched off for insertion @cite_18 . Furthermore, the ad hoc constraint management solutions are heavily dependent on user input based on a priori knowledge of the type of contact surfaces, which are in turn limited to simple categorized classes of geometric features---e.g., coplanarity of prismatic mates, coaxiallity of cylindrical joints, and alike. In a similar classification to the one stated earlier for CD methods, the existing constraint identification algorithms can be identified as combinatorial methods that scale in running time with the complexity of the input CAD models, and look for certain heuristic indicators of a match between complementary features.
@cite_18 @cite_49 @cite_2
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Purpose – The paper aims to present interactive simulation with haptic feedback as a valid method for solving complex assembly problems in the context of industrial product development. Its purpose is to clarify the position of interactive simulation with respect to other methods, and to emphasize its specific value for design engineers.Design methodology approach – The paper describes the challenges faced by design engineers in the context of design for assembly and assembly process planning. It introduces and compares automatic path planning and interactive simulation as two different approaches for checking the feasibility of assembly tasks. It provides a review of the scientific challenges and technical issues faced when implementing interactive simulation with haptic feedback in this context. It presents recent research results in the domains of final insertion and human model simulation.Findings – The paper provides an overview of the scientific, technological and practical aspects of interactive si... This research presents a novel approach to virtual assembly that combines dynamic modeling with geometric constraint-based modeling to support low clearance manual assembly of CAD models. This is made possible by utilizing the boundary representation solid model data available in most contemporary CAD representations, which enables (a) accurate collision physics calculations on exact model definitions, and (b) access to geometric features. Application of geometric constraints during run-time, aid the designer during assembly of the virtual models. The feasibility of the approach is demonstrated using a pin and hole assembly example. Results that demonstrate the method give the user the ability to assemble parts without requiring extensive CAD preprocessing and without over constraining the user to arrive at predetermined final part orientations. Assembly is successful with diametral clearance as low as 0.0001 mm, as measured between a 26 mm diameter hole and pin. Over the years, various approaches have been investigated to support natural human interaction with CAD models in an immersive virtual environment. The motivation for this avenue of research stems from the desire to provide a method where users can manipulate and assemble digital product models as if they were manipulating actual models. The ultimate goal is to produce an immersive environment where design and manufacturing decisions which involve human interaction can be made using only digital CAD models, thus avoiding the need to create costly preproduction physical prototypes. This paper presents a framework to approach the development of virtual assembly applications. The framework is based on a Two Phase model where the assembly task is divided into a free movement phase and a fine positioning phase. Each phase can be implemented using independent techniques; however, the algorithms needed to interface between the two techniques are critical to the success of the method. The paper presents a summary of three virtual assembly techniques and places them within the framework of the Two Phase model. Finally, the conclusions call for the continued development of a testbed to compare virtual assembly methods.Copyright © 2011 by ASME