Experimental study on four rotor helicopter 10 m-range distance and position measurement method by using two searchlights for autonomous control and the evaluation
Abstract
This paper reports experimental result of a distance and position measurement method for autonomous movement control of four-rotor helicopters (drones) that uses two spotlights and comparing with a red marker using case, discuss the results of autonomous flight test evaluations. To conduct autonomous drone flights exceeding 10 m under unstable GPS signal situations, such as under bridges or inside tunnels during periodic maintenance inspections, correct self-positioning measurements are indispensable. This study proposes a simple method whereby autonomous drone movement control can be performed over distances exceeding 10 m by using two high-power 100 V alternating current spotlights set on the ground as infrared (IR) light sources. The spotlights are directed at the investigation target, such as the cracked area of a bridge, and the intense light of the two spotlights provides reference points that enable the drone to determine its correct position. In autonomous flight-testing in an enclosed corridor, our method provides capable of determining the drone’s position at distances up to 15 m with a standard deviation of 0.31 m. Our proposed method would be effective in situations where no skilled drone control operator is available and for flights requiring visual cue confirmations under adverse outdoor conditions.
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Introduction
In this paper,a distance and position measurement method for autonomous movement control of four-rotor helicopters (drones) that uses two spotlights and discuss the results of a related autonomous flight test evaluation. To achieve drone flights in excess of 10 m under unstable global positioning system (GPS) signal situations, such as under bridges or inside tunnels and buildings during periodic maintenance inspections, an easy and precise self-positioning measurement method is indispensable for stable control [1,2]. This is because, even if a drone is human controlled, it is difficult for an operator to manipulate the device in flight at distances in excess of 10 m using visual cues alone [3-12]. In those situations, other supporting mechanisms are necessary for drone control and position measurements [3,4,13-26]. The aim of this study is to propose a simple method whereby autonomous drone movement control can be performed over distances exceeding 10 m by using two high-power 100 V alternating current (AC) spotlights set on the ground as infrared (IR) light sources (Fig. 1) and it is comparing with the general method of using a red colored marker board attached to the drone. In our method, the spotlights are directed at the investigation target position, such as the cracked area on the side of a bridge [2].
Since drone helicopters are seldom equipped with internal autonomous position controls, ground-based positioning systems based on IR light sources, three-dimensional (3D) cameras, or GPS sensors are needed control their positions during flight [10,11,22-28]. In the case of methods using IR or 3D cameras, the position measurement precision can be on the order of 1 mm, but these methods are normally restricted to indoor situations at distances less than 10 m [5,13]. On the other hand, if a drone is being controlled in an outdoor situation, GPS signals can be used as long as there are limited numbers of obstacles in the skyward and movement directions. However, when using a drone for periodic inspection under bridges or inside tunnels, neither of the abovementioned two approaches can be adopted because distances tend to be excessive and GPS signal reception under bridges or within tunnels is often unstable [2]. If a drone position is detected based on visual cues, cameras can be used to measure its position. This is known as visual-servo control [26-29]. However, in situations where there are numerous obstacles in the camera image, it is difficult for the controlling operator to ascertain a drone’s position based on camera imagery alone, especially at distances in excess of 10 m from the starting point.
Conclusion
In this paper, a 10 m-range autonomous four-rotor helicopter (drone) movement control system that utilizes two high-power spotlights was proposed and autonomous flight test evaluations were performed. To realize drone flights in excess of 10 m under unstable GPS signal situations, such as under bridges or inside tunnels during periodic maintenance inspections, the ability of a drone to perform correct self-positioning measurements is indispensable for stable control. In our experiments, distance measurements were more stable when two spotlights were used in comparison to experiments conducted with a single spotlight and those conducted with a red marker attached to the drone. And the 15-m-long distance measurement precision of the drone position shows an SD of 0.31 m. Our proposed method would be effective in situations where no skilled drone control operator is available and when flights requiring visual confirmation under adverse conditions are required.