Development of High-accuracy Multi-degrees-of-freedom Indoor Ultrasonic Positioning Approach for Automated Guided Vehicles

GPS has been offering commercial outdoor positioning services. However, it is not suitable for indoor positioning purposes because of the weak satellite signals indoors. Therefore, the ultrasound technology has been developed and applied to indoor positioning for automated guided vehicles (AGVs) or moving robots. Unfortunately, traditional trilateral ultrasound methods usually suffer from a narrow coverage range and low accuracy. For this reason, we firstly systematically analyze the effects of ultrasound wave loss on positioning and those of the ultrasonic signal receiving angle. On the basis of fundamental information, a multi-degrees-of-freedom (Multi-DoF) ultrasonic positioning system is then proposed. The Multi-DoF system is constructed using two steering engines, where one has a 360-degree horizontal rotating angle and the other one has a vertical rotating angle greater than 180 degrees. Accordingly, it can efficiently receive all signals from the ultrasonic transmitting device of a moving AGV. Experimental results confirm that the proposed method can reduce the average positioning error to 3.2 cm, significantly improving the accuracy compared with existing trilateral methods.