| In recent years,with the development of quadcopter UAV technology,UAV is utilized in more and more domains to perform some dangerous or pressing tasks,such as border patrol,forest fire prevention,disaster re scue,power patrol,etc.As a key technology to achieve above tasks,positioning method is essential for UAV and GNSS is the widely used at present.But due to the influence of GNSS navigation error,quadcopter UAV can hardly land to the designated landing area,which causes a failure of outdoor UAV automatic landing and charging limits the work effective and flight range of UAV.And if the UAV is controlled by personnel operation,it may collide with other objects and crash out of control due to inaccurate control.In order to solve the problem,two new structures of electromagnetic positioning and navigation system are proposed and designed in this paper base on the improvement of traditional6-DOF electromagnetic positioning model to replace the GNSS to navigate the UAV landing near the landing area.First of all,the base principle and hardware structure of electromagnetic positioning system are analyzed and the 6-DOF positioning algorithm is derived from magnetic dipole model based on matrix and vector operation.Then according to the requirements of close accurate position and navigation,this paper analyzes the advantages and disadvantages of traditional electromagnetic positioning system and proposes basis and strategy for improvement.On this basis,this paper proposes and designs two new structures,which are multiply electromagnetic field generators structure and multiply electromagnetic field sensors structure.These two systems have different design schemes.For multiply electromagnetic field generators structure,its characteristics are as follows:(1)It is composed of several electromagnetic field and one electromagneticfield inductor.The generators are arranged in the landing area according to certain structure,and the electromagnetic field inductor is carried by UAV.(2)Each electromagnetic field generator is composed of three mutually orthogonal coils,and the electromagnetic field inductor is composed of three mutually orthogonal sensors.The coils and the inductors are needed to switch repeatedly to obtain complete measurement signal when the system is working.(3)The signal processing circuit amplifies the measured signal and uses band-pass filtering,full wave rectification and low-pass filtering to process the signal successively to obtain the DC signal,and then the ADC samples it(4)By using the DC signal sampled by the ADC,the electromagnetic positioning system model and the nonlinear least square method,the coordinate of the electromagnetic field inductor is calculated to realize the positioning of the UAV and navigate the UAV to the landing area.For multiply electromagnetic field sensors structure,its characteristics are as follows:(1)It consists of an electromagnetic field generator and an electromagnetic field inductor.The electromagnetic field generator is at the center of the landing area,and the electromagnetic field inductor is also carried by the UAV.(2)The electromagnetic field generator is composed of a z-axis coil,and the electromagnetic field inductor is composed of several electromagnetic field sensor modules.Each sensor module contains a three-axis cubic coil and a weak signal amplifier.The switching between the sensor modules is needless during operation,which means all coils can work at the same time.(3)The signal is sampled by ADC,processed by the filter algorithm in the processor,and finally the signal amplitude of specific frequency is calculated by FFT.(4)By using FFT to calculate the signal amplitude,using a simplified electromagnetic positioning system model and using nonlinear least square method to calculate the azimuth angle of electromagnetic field inductor to realize the orientation of UAV and navigate the UAV to the landing area.In addition,resonance circuit is used in the above systems to reduce the power consumption and improve the signal-to-noise ratio of the system.At the same time,due to the adaptive adjustment method of system parameters based on Kalman filter prediction,the system can timely change the key parameters of the system,prevent the output saturation of the sensor circuit on the basis ofobtaining the maximum signal-to-noise ratio,and ensure the highest measurement accuracy.Finally,for the new systems,the relationship between the noise of signal processing circuit and the gain of the system,the signal-to-noise ratio of the system,the ranging capability and the ranging error are measured,and the flight experiments are also carried out.For multiple electromagnetic field generators structure system,the experimental results show that the static ranging error is less than 2cm when the electromagnetic field inductor is within 1m of the electromagnetic field generator.And For multiple electromagnetic field sensors structure system,the experimental results show that the average measurement angle error of the system azimuth is less than 3° when the relatively height is less than 110 cm,especially when the electromagnetic field inductor is within 1m of the electromagnetic field generator,the azimuth angle error is less than 1 °and the corresponding horizontal radian error is less than 1.8cm.The flight experiments verify the positioning and navigation ability of the two electromagnetic positioning and navigation systems in the actual environment under various noises,and due to these noises in the flight experiment,the flight measurement accuracy has certain randomness.Experiments show that each system can complete the mission independently,realize the close-range accurate positioning navigation for quadcopter UAV. |
PDF Full Text Request