Analysis and procedures for design of diaphragm chucks

In modern automated manufacturing systems, there is a need for work-holding devices that provide for precision, accuracy, reliability, flexibility and remoteness of control. One of such devices is the diaphragm chuck which utilizes the strain energy of its varying thickness diaphragm plate for gripping action. The jaw-carrying diaphragm plate is deflected by a thrust load, and the jaws are bored or ground to the nominal diameter of the workpiece. Gripping action occurs when the workpiece is inserted into the jaws and the thrust is relieved. Designers and manufacturers of diaphragm chucks have in the past been limited to the use of empirical data for diaphragm chuck design. This design limitation has been caused by complex problems due to factors such as the varying thickness encastre diaphragm plate, the gripping couples and the stiffening effects of the jaw slides. This work involved the establishment, by theory and experimental verification, of the design and performance parameters of a diaphragm chuck, and the provision of diaphragm chuck design methodology. The designer is therefore able to achieve the a priori design of the diaphragm chuck. In addition, the user is able to adapt existing diaphragm plates to achieve required gripping forces within existing constraints. The scope of this research is the static gripping action for any number of symmetric jaws. The design method is for diaphragm plates with small thickness taper, and carry detachable jaw slides. The concept of the equivalent constant thickness is applied to the diaphragm plate. Gripping action is divided into two major phases - the separate deflections of the diaphragm plate by a thrust load and symmetric couples. These deflections are equated to obtain the gripping force. This research concludes that the gripping force of a diaphragm chuck is closely predicted by the equivalent constant thickness method. Design data and methodology are provided for diaphragm chuck design. Thus, a designer can now design a diaphragm chuck based on a desired and pre-specified gripping force requirement.