A Flexible Robot System for Assembly with a Concept of Holon

　In the recent times, production styles are changing from mass production of a few kind of product to production of various products in small quantity. Traditional manufacturing systems cannot deal with this new production style, because they do not have flexibility; fault-tolerance, multipurpose, response to the active change of production schedules, or quick restart at the change of products, etc. Then flexible manufacturing systems are studied.

In this research, we focus on assembly among various manufacturing activities, and aim to construct flexible assembly system using multipurpose robot manipulators. The concept of Holon is applied to our system in order to make it flexible.

Holon is autonomous and cooperative component of a system. Holons construct "holarchy" (hierarchical control architecture) to execute jobs. In our system, the holarchy has four layers (Fig.1). The upper three layers, which consist of "management holons"--task holons, process holons, and operation holons, deal with manufacturing. The bottom layer consists of execution holons, which correspond manufacturing devices one by one. Communications between management holons and execution holons are performed according to contract net protocol.

First task holon is ordered to assemble a certain product. As the order is delivered into lower layers, it is divided into a number of smaller jobs. Then operation holon, which is in the bottom of management holons, is ordered to transfer a part or assemble two parts into one. Operation holon carries out this job using appropriate execution holons.

We implemented our system to an assembly cell and experimented on production of products (Fig.2). As a result, it turned out that our system can deal with active change of production schedules.

We also propose "Plug & Produce"; a concept of a manufacturing system where manufacturing devices can be easily added or removed without terminating the whole system. We implemented this concept to the assembly cell and added a new manipulator in the middle of a production activity. The new manipulator immediately joined the assembly.

Keywords: Holonic Manufacturing, Manipulators, Assembly Cell

Fig. 1 Holarchy of the system 　　　　　Fig. 2 Assembly cell