Abstract
Workholding is an essential and unavoidable activity in an automated manufacturing environment. Workpiece fixturing on machine tools is one common example of workholding. Part grasping by a robot is another. In this paper, a new and more general verification system is developed and presented. To ensure complete motion restriction of a workpiece during machining, assembling, transporting, or other processes, resultant force and moment must be zero. The proposed model consists of several considerations, i.e. (1) time-varying acting and reacting force equilibrium, (2) limits of force magnitudes to prevent excessive deflection, (3) constraints of force directions based upon the part geometry, and (4) frictional effects. Based on these considerations, the verification system is modeled as a quadratic optimization problem. A computer program is developed to demonstrate the capability of this model. A given workholding configuration for a specific part geometry is verified when a solution of the model exists. The hidden reactive forces are computed for further deflection analysis. The immediate application of this verification system is to check the validity of the fixture configuration in a computer-aided interactive fixture design system. Further application is underway in developing fully automated fixture design methodology. Section 1 of this paper reviews the previous literature related to workholding verification, especially in workpiece fixturing. In Section 2, a new approach to workholding verification is developed to ensure the validity of the workholding configuration. Quadratic programming is applied to construct the general verification models in Section 3. Section 4 gives a numerical example to illustrate the verification concept in fixture design. Finally, a summary is presented in the last section.