Ensuring fault tolerance of robotic systems is a challenge for factory automation. This paper focuses on multi robot manipulation and maintenance for fault-tolerant systems. For this purpose, a manipulation strategy of multiple mobile robots, that enables a system to continue operating even if a working robot undergoes preventive maintenance or fails and undergoes corrective maintenance, is implemented. In addition, a robot failure and a maintenance policy for preventive and corrective maintenance activities are mathematically modeled on the basis of reliability engineering. Thus, working robots are allowed to undergo preventive maintenance at an optimal interval and corrective maintenance each time they fail. Finally, through simulation experiments, the effectiveness of an integrated multi-robot manipulation and maintenance in industrial applications is shown.

This paper focuses on the effectiveness of maintenance in fault-tolerant multi-robot systems. Such a system is enabled to work as long as one robot works; namely, completely parallel. For this system, it is required to ensure fault tolerance and maintain high performance taking robot failures and maintenance, such as prevention and correction of robots, into account. Therefore, we propose an optimal maintenance strategy on the basis of reliability engineering. This strategy enables robots to undergo preventive maintenance at optimal intervals and corrective maintenance each time they fail. Through simulation experiments, the effectiveness of the optimal maintenance strategy is investigated. In addition, the influence of robots undergoing maintenance on system performance is mathematically and experimentally discussed on the basis of the number of robots and maintenance strategies.

This paper describes a methodology regarding an autonomous cruise control (ACC) of circulating multi-robot which is directly effective for solving the congestion regardless of the presence of a bottleneck. For this purpose, we focus on an external interaction force between the robots. This force is generated with the use of a virtual damper. In this methodology, two control scenarios are presented: a damping force acts on a moving robot as the external interaction force, (I) only when its preceding robot(s) is/are stopping or being congested and (II) when a robot exists in front of the moving robot, in order not to become involved in the congestion. This paper deals with a circuit and a robotic manufacturing-transportation system for industrial automation. Through simulation experiments, it is shown that the proposed ACC successfully solves the congestion, and finally, improves the throughput. In addition, the superiority of the two control scenarios, ACCs (I) and (II), is discussed.

In this paper, we focus on a batch manufacturing system with multiple industrial robots. In this system, material-handling robots (MHRs) and material-processing robots (MPRs) are operating. Since various operations are conducted at certain places, one of them might include a localized bottleneck. A localized bottleneck is a constraint that dominates the maximum amount of production in a system, that is, the productivity. In addition, the bottleneck induces congestion; as a result, the productivity declines. For these issues, there are two primary challenges: bottleneck prevention and restraint. To solve them, suitable operational techniques with respect to the MHRs and MPRs are needed in order for them to operate appropriately while relating to each other. In this paper, a constructive approach toward multi-robot coordination problems is taken. In this approach, we propose applicable operational techniques for the robots. Through simulation experiments, we examine the effectiveness of the proposed techniques and their combinations and, finally, show an integrated operational technique. Each of the operational techniques solves a localized bottleneck and the congestion, and the integrated technique successfully improves the productivity and results in the most efficient system.

This paper focuses on an automated batch manufacturing system with material-handling robots (MHRs) and material-processing robots (MPRs). In this robotic manufacturing system, materials transported by the MHRs are processed by the MPRs. These operations cause a bottleneck in the system. Furthermore, the bottleneck induces congestion of the MHRs. In the system, the effect of an operational delay due to bottlenecks affects the entire operation. Accordingly, there is an event in which the congestion extends and the system throughput not only fails to increase but also may become worse, even if more robots are used to improve the productivity. For this challenge, we propose a behavior control method for the MHRs to eliminate or ease the congestion that arises from a bottleneck. Each MHR controls its own behavior adequately by using the external force of a virtual damper in order not to become involved in the congestion. Finally, through a simulation experiment, we show that the proposed control method improves the system throughput and its effectiveness for a more efficient system operation.

Modeling and impedance control of a microgripper which comprises a pair of cantilever plates actuated by piezoceramics are addressed. An analytic model is first derived and then experimen- tally identified. Position-based impedance control is implemented to specify the mechanical impedance of the tip of the cantilever plate, incor- porating a type 1 servo and a low pass filtered force feedback. Stability analysis of the impedance con- trol is made to clarify the specific limitations of the designed structure and controller. The position servo is designed to achieve stable impedance con- trol for a wide range of environmental stiffness and impedance parameters. Experimental verification of the analysis and gripping force regulation are demonstrated.