Microhandling devices for the assembly of Hybrid Microproducts
PhD Thesis Marcello Porta
Abstract
Hybrid microproducts are very important in every application where small dimension and light weigh are fundamental. They are used in different fields, such as the automotive, the aeronautic/aerospace, the automation, the medical and biomedical field, the watch industry, but also in the sport and entertainment sectors.
These microproducts differ from MOEMS because they consist of several components with some features of few hundreds microns made of different materials. The final product is obtained by the assembly of the various components and this gives hybrid microproducts a high 3D aspect and better mechanical performance than MOEMS.
The main problem that limits the market diffusion of these products is the enormous assembly cost that represents up to the 80% of their final cost. This is due to their manual assembly that is a time consuming activity. Actually, traditional assembly systems are not suitable because when dimensions of objects are less than 1 mm, many problems arise:
surface forces become bigger than gravity, there are difficulties due to the vision and force control, objects can be fragile, tolerances become very narrow, there is not a systematic design for microassembly, methods and models are not developed enough in microdomain.
Different approaches can be found in literature as an alternative to manual assembly to reduce costs. One of the most promising strategies is the assembly microfactory. It is a miniaturization of an assembly system with the aims of improving precision and reducing the ratio, in terms of energy, material and space consumption, between the assembly facilities and the microproducts obtained. Therefore, many assembly and control devices have to work in a very little area with low energy consumption and high precision.
Nowadays, one of the main problems that makes difficult the development of these microfactories is the lack of handling devices able to manipulate components that have dimension of few hundreds microns. The required handling devices are microfeeders to transport, orient and position microparts, microsorters to arrange components, microgrippers to grasp and release them, micromanipulators and microrobots to support microgrippers.
In the PhD research activity various innovative handling devices for manipulating parts of different materials and shapes have been designed, developed and tested. These systems are able to solve some critical issues in the automatic handling of objects with dimensions of few hundreds microns such as feeding and transporting, grasping and releasing, positioning. The developed systems are an electrostatic centering device and an electrostatic sorter, some mechanical and adhesive grippers and a 2 DOF microrobot.
The two electrostatic devices make use of electrostatic force to transport and position microparts (the centering device) and to sort and arrange a group of objects randomly positioned (the sorter system). Two kinds of gripper have been designed: the mechanical (piezo actuated) and the adhesive gripper. The first kind uses a piezoelectric actuator to
Microhandling devices for the assembly of Hybrid Microproducts
PhD Thesis Marcello Porta
close and open the fingers, the second exploits capillary forces to grasp and center microobjects. Finally, the 2 DOF manipulator is an electromagnetic device able to support light grippers as electrostatic and adhesive ones.
These devices have been integrated in the assembly microfactory in progress at the Department of Mechanical, Nuclear and Production Engineering of the University of Pisa within the Italian research PRIN project “Development of innovative technologies for the assembly of hybrid microproducts”. In this microfactory, the assembly strategy makes use of a carrier that contains the components of the products to be assembled and moves from an assembly station to the next one. This assembly system is confined in a controlled environment and consists, at the moment, of an assembly station equipped with various grippers (on the basis of the assembly tasks to be carried out) and controlled by vision systems.
