IRIS-97-359

A Potential Field Method for the Automatic Design of Modular Fixtures

Kamen Penev

A fixture is an arrangement of fixturing modules that locate and immobilize a workpart during a manufacturing operation such as machining, inspection, or assembly. Modular fixtures are assemblies of standard fixturing components such as mounting plates, raisers, bars, struts, clamps, or supports, selected from an extensive toolkit. Automatic design of modular fixtures consists of determining which fixturing modules to select, how to set their parameters, how to compose them in functional units, and where to place them so that the result is a workholding setup adequate for the given workpart and manufacturing operation. The process of designing a fixture is decomposed into three consecutive phases: analysis, contact placement and layout design.

We propose to use areas of repulsion and attraction on the workpart boundary as a universal means of representing fixturing information. The algorithm simulates a potential field defined by these areas and performs a series of relaxation epochs of initially random configurations of contacts. Each contact is regarded as a charged particle that repels the other contacts within a certain distance. Starting with a minimal configuration, the number of contacts is subsequently increased if a certain number of epochs are unsuccessful. Thus, a solution will be found for any part, although this solution may include redundant fixels. The simplicity of the potential field method allows for a very efficient implementation. Experiments with a 2D implementation resulted in consistent success in time well below one second. The 3D algorithm performs in times of the order of several seconds on a conventional workstation.

We designed and implemented a fixture layout procedure that configures fixture templates, such as overhead clamps or vertical supports, that implement the contact points. All contact points are classified into four types: vertical supports, side locators, side clamps, and overhead clamps. Parametric templates of each of these categories are then selected and configured so that the contacts are attained by the areas of application of the instantiated templates.