ComputerAided_Design_Engineering_amp_Manufactur.pdf

FIGURE 3.2
and CAD/CAM, which are essential ingredients of modern manufacturing. Figure 3.2 shows a schematic
diagram highlighting the approaches that have received significant attention in the past decade. 6 These
approaches are briefly described in this section.
Sensory-Based Workholding Techniques
In order to reduce the accuracy requirements for workholding, sensory-based information may be used
to compensate for positioning errors in an assembly setup. Machine vision techniques have been applied
to manufacturing processes to create a “visual fixture.” Visual fixturing utilizes triangulation-based formulations
and computer control to generate a workpiece “offset matrix” for use by a robot controller.
The matrix effectively defines the location of the workpiece in six degrees of freedom. This technique
has been applied to the fixturing problem encountered for insertion of windshields onto automobile
bodies. It must be noted that this is a method to correct for location errors on parts for which traditional
fixtures have already provided adequate clamping.
Modular and Reconfigurable Fixtures
Modular fixturing employs a number of elements such as V-blocks, rectangular blocks, and clamps to
construct a fixture layout. 7 These pieces are bolted down to a T-slotted plate or a base plate with plain
and tapped holes. The plate is usually part of the machine bed. The elements are aligned precisely with
the aid of measuring devices (e.g., height gauge). Toggle clamps are often used to allow for rapid changing
of the workpiece. The clamps push the workpiece against the V-blocks and rectangular blocks, thus
constraining the workpiece. The accurate alignment of the workpiece requires great care.
Modular fixturing kits are based on the traditional machinist’s approach of developing a variety of
fixtures by assembling primitive elements. 8 Research efforts in modular fixturing have focused on the
development of strategies for automatic setup of these elements using robots. Efforts have also been
aimed at developing computer-assisted design techniques and geometric reasoning for assembly of the
elements. 9–14
The concept of reconfigurable fixtures has received considerable attention. 6 This approach uses a
number of modules or mechanisms that are reconfigured or rearranged to form layouts that position
© 2001 by CRC Press LLC
Flexible workholding strategies. (Reprinted from Reference 5, with permission from Elsevier Science.)