Experimental evaluation of a special purpose miniature machine tool with parallel kinematics architecture: Free leg hexapod

This paper reports on multi-scope evaluation of the special purpose in situ parallel kinematics machine tool known as the Free-Leg Hexapod or FreeHex. The process and equipment used to calibrate the machine and determine the positions of its lower joints in relation to each other and the feature to be machined are explained in detail. The need to match the machine's working envelope to a feature to be processed is highlighted and solutions are presented in the form of theoretical models which build upon those presented for the kinematics and work volume of the machine and relate them to a target feature. One model generates a range of configurations for processing a given feature, the other checks the viability of specified configurations. Experiments are presented which verify the various theoretical models; it was determined that all the proposed models provide an acceptably accurate representation of the FreeHex system. In addition, a range of experimental work to evaluate the positioning and machining accuracy of the FreeHex prototype is presented. It is demonstrated that the FreeHex has successfully evolved from an innovative concept to a versatile and functional machine capable of in situ operations.