The development of a generic and effective force model for semi-automatic or manual virtual assembly with haptic support is not a trivial task, especially when the assembly constraints involve complex features of arbitrary shape. The primary challenge lies in a proper formulation of the guidance forces and torques that effectively assist the user in the exploration of the virtual environment (VE), from repulsing collisions to attracting proper contact. The secondary difficulty is that of efficient implementation that maintains the standard 1 kHz haptic refresh rate. We propose a purely geometric model for an artificial energy field that favors spatial relations leading to proper assembly, differentiated to obtain forces and torques for general motions. The energy function is expressed in terms of a cross-correlation of shape-dependent affinity fields, precomputed offline separately for each object. We test the effectiveness of the method using familiar peg-in-hole examples. We show that the proposed technique unifies the two phases of free motion and precise insertion into a single interaction mode and provides a generic model to replace the ad hoc mating constraints or virtual fixtures, with no restrictive assumption on the types of the involved assembly features.
The PBM functionalities in virtual assembly applications (including collision response, impact friction mechanics, and noon-smooth Lagrangian dynamics @cite_3 ) are typically offered as part of a physics simulation engine (PSE). Although a PSE+CD approach seems the most natural choice (at least in theory) for a virtual mimicry of real-world constrained motion, it is not effective in practice for final insertion in low-clearance assembly @cite_30 @cite_48 . This arises for at least two reasons: 1) numerical errors due to the approximate representations used in fast CD methods popular for haptic rendering; and 2) input noise due to hand vibrations and device errors. The former can be solved by using exact representations, which comes at the expense of computational burden. For example, later versions of SHARP @cite_51 @cite_45 employed the collision detection manager (CDM) module of D-Cubed, which makes direct use of Boundary Representation (B-rep) of CAD models. However, the latter difficulty persists, even with exact CD.
@cite_30 @cite_48 @cite_3 @cite_45 @cite_51
2022891348 2159923417 2086019095 2148336640 1971764625
Virtual Reality (VR) technology holds promise as a virtual prototyping tool for mechanical assembly; however, several developmental challenges still need to be addressed before virtual prototyping applications can successfully be integrated into the product realization process. This paper describes the development of SHARP (System for Haptic Assembly & Realistic Prototyping), a portable VR interface for virtual assembly. SHARP uses physically-based modeling for simulating realistic part-to-part and hand-to-part interactions in virtual environments. A dual handed haptic interface for realistic part interaction using the PHANToM® haptic devices is presented. The capability of creating subassemblies enhances the application’s ability to handle a wide variety of assembly scenarios. Swept volumes are implemented for addressing maintainability issues and a network module is added for communicating with different VR systems at dispersed geographic locations. Support for various types of VR systems allows an easy integration of SHARP into the product realization process resulting in faster product development, faster identification of assembly and design issues and a more efficient and less costly product design process. Virtual reality (VR) technology holds promise as a virtual prototyping (VP) tool for mechanical assembly; however, several developmental challenges still need to be addressed before VP applications can successfully be integrated into the product realization process. This paper describes the development of System for Haptic Assembly and Realistic Prototyping (SHARP), a portable virtual assembly system. SHARP uses physics-based modeling for simulating realistic part-to-part and hand-to-part interactions in virtual environments. A dual-handed haptic interface for a realistic part interaction using the PHANToM® haptic devices is presented. The capability of creating subassemblies enhances the application’s ability to handle a wide variety of assembly scenarios at the part level as well as at the subassembly level. Swept volumes are implemented for addressing maintainability issues, and a network module is added for communicating with different VR systems at dispersed geographic locations. Support for various types of VR systems allows an easy integration of SHARP into the product realization process, resulting in faster product development, faster identification of assembly and design issues, and a more efficient and less costly product design process. In the context of virtual reality, haptic interfaces are coupled with simulations, which treat interactions between objects. To simulate contacts or impacts, we focus our attention on simulators based on dynamics for rigid models. In this article, we first propose a brief state of the art on closed-loop haptic interaction. Then, we discuss the use of non-smooth dynamics methods for interactive, haptic-based simulations. We finally present our research software, which proposes a haptic interface coupled with non-smooth dynamics algorithms. 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. This research combines physics-based and constraint-based approaches for virtual assembly simulations where geometric constraints are created or deleted within the virtual environment at runtime. In addition, this research provides a solution to low clearance assembly by utilizing B-Rep data representation of complex CAD models for accurate collision physics results. These techniques are demonstrated in the SHARP software (System for Haptic Assembly and Realistic Prototyping). Combining physics-based and constraint-based techniques and operating on accurate B-rep data, SHARP can now assemble parts with 0.001 clearance and can accurately detect collision responses with 0.0001mm accuracy. Case studies are presented which can be used to identify the suitable combination of methods capable of best simulating intricate interactions and environment behavior during manual assembly.Copyright © 2007 by ASME