Mini-Robotic Applications for Miniaturized Assembly Tasks

Nowadays the Robotics is a discipline widespread in lots of industrial contexts: it has become essential for the production of goods and for the improvement of processes since it reduces the factory costs allowing to orientate the manufac­turing to solutions of mass production without renouncing the customization of the final products. This is possible thanks to the wide flexibility the use of automated devices brings. But when the scale of the objects to manipulate de­creases, the tolerances of machining increase and many points of the workspace are inaccessible - to the human hands it is important to have the right devices in order to carry out the desired manufacturing processes.In these circumstances it is essential to introduce the new solutions that the research is developing for solving the previous problems: their use entails a series of aspects that are negligible for the macro world while are at the basis of the "Minirobotics", such as the important role that in these contexts is assumed by electrostatic forces, adhesion forces and van der Waals forces.This dissertation aims to introduce two examples of Miniwrist studied by the Machine Mechanics Group of the Department of Mechanics of the Faculty of Engineering of the Polytechnic University of Marche, one of which is actually in rapid prototyping process phase. The research, funded by the Italian Ministry of Research and Education (MIUR) within the PRIN2005 Project, has started three years ago with the study of a parallel tripod architecture able to guar­antee the rotation of the mobile platform around three orthogonal axes: this spherical wrist, characterized by the kinematic sequence of pairs Cylindrical­-Revolute-Universal for each leg (3-CRU), has been the subject of an accurate kinematic, static and dynamic characterization that allowed to approach con­sciously to the following design phase. It is interesting to highlight how the really innovative aspects of the minirobotics are those regarding the designing. The necessity to scale the dimensions of the robot to millimeter level constrains the researchers to resort to new techniques for the machining of components and for the realization of joints; this is testified by the current rapid spread of the flexures technologies which exploit the compliance of the material in order to allow the relative rotation between the limbs of devices and by the rising of new technologies such as tbc Electro-Discharge-Machining (EDM), the LIGA technology, the laser cutting and others.The study of these topics has been indispensable for the following kineto­static synthesis of the wrist that was carried out by means of FEM software. The aid of FEM tools integrated in the multibody software "VirtuaL.Lab" has allowed to run static and dynamic simulations considering the stiffness of all the parts with particular attention to the flexible joints one: these tools have assisted the designing of the 3-CRU thus the drawing of a monolithic structure having the compliance localized mainly in the proximity of the virtual hinges. Unfortunately, even if a detailed process of adjusting was carried out on the design of the device, some drawbacks related to the translation of the centre of motion and to the appearance of undesired warping phenomena have driven our interest towards a new kind of architecture. The wish of getting a prototype of the chosen minirobot has turned our attention to a structure suitable for being realized in small dimensions: it is no more a spherical wrist but a simpler 2 dof pointing device that is made of a mobile platform which is free to rotate around a universal joint and is sideways driven by two actuators. In this case the compliance of the whole mechanism is localized in the centre of the joint which mechanical behaviour determines some important parameters such as the workspace and the maximum thrust.The study of this device has followed the same steps of the previous one: af­ter a preliminary kinematic synthesis of the suitable architectures the attention focused on the one just described. Complete kinematic and static analyses were carried out and at last, after having determined the values of the geometrical parameters by means of an optimization procedure, a detailed designing approach , aided by a virtual prototyping environment, has allowed to determine the final structure of the pointing device.