This paper describes the leader-follower formation control using two different approaches which are the PID leader-follower formation control (PID-LFFC) and Sliding Mode Control leader-follower formation control (SMC-LFFC). The strategy used in this paper is to apply the control algorithm for conducting a circular motion. This task is known to be important since a trajectory is a combination of movement. This movement can be divided into straight or curve lines. Curves lines or circular motion is essential for obstacle avoidance and also for turning movement. The curves lines or circular motion gives lower trajectory distance than only using straight or angled lines. Based on the experimental result, it is seen that the performance of the algorithm is reliable. When using SMC-LFFC over the PID-LFFC, the leader to follower distance error is 30% smaller and has a high 70% occurrence at 0 errors. Additionally, this research is known to be the first conducted in Japan.
[abstFig src='/00280006/14.jpg' width='250' text='Fault tolerant control structure of hexacopter' ] This paper presents a fault-tolerant approach for the propulsion systems of hexacopters (i.e., rotors and propellers) to overcome failures during outdoor autonomous flight missions. In this study, we used an explicit control allocation method for each stopped motor, and an asymmetrical motor rotation arrangement is applied in order to guarantee the controllability of the yaw. Finally, the developed fault diagnosis and isolation system is tested during a global-positioning-system-based autonomous flight of a hexacopter with a failed motor.
The accuracy of small and low cost GPS is insufficient to provide data for precisely landing Micro Air Vehicles (MAV)s. This study shows how a MAV can land on a small targeted landing site by using sensors rather than imprecise GPS data. This paper describes a proposed movable range finding sensor system for measuring the environment and an algorithm of position measurement. This range finding system consists of four Infrared (IR) sensors, four servo motors and one ultrasonic sensor. In order to measure the MAV's position, the sensor system vertically swings each IR sensor using the servo motors and these IR sensors detect the edge of landing target. And this sensor system calculates the position from the measured edge direction and the ultrasonic altitude. Additionally, experiments of autonomous hovering over a 52cm × 52cm table and autonomous landings were carried out indoors using the proposed sensor system. Our experiments succeeded, and as a result, the MAV kept flying horizontally within a 18cm radius circle, and then it landed on the table from a height of 50cm. The IR sensors were selected because of the payload limitations of small MAVs. If the MAVs' payload capacity were higher than a laser sensor, then it would be used, since the lasers can operate better in sunlight than IR sensors and also they tend to have longer scanning ranges and are more accurate.
[abstFig src='/00280006/18.jpg' width='300' text='Hovering with 5 rotors' ] This study presents a fault-tolerance approach for hexacopters with failed propulsion systems (i.e., motors and propellers) using sliding mode control theory. In this study, we use an explicit control allocation method with linear constraints for allocating the control input to redundancy actuators, as well as a new sliding model controller designed to stabilize the attitude and maintain the basic flight performance of a vehicle with a single failed motor during an outdoor autonomous flight mission. An asymmetrical motor rotation arrangement is applied in order to ensure controllability for all degrees of freedom. We verify the developed system on a real hexacopter suffering propulsion-system failure. Finally, the comparative results between the linear-quadratic-integral controller and model reference sliding mode controller are presented to evaluate the robustness of each controller against the failure of redundancy actuators.
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