Research On Braking Method Of Fixed Wing UAV Braking System For Anti-sideslip And Short Distance

Rolling braking is one of the critical links in controlling fixed-wing UAVs.Insufficient braking system design will lead to accidents such as rollover and overrunning the runway,which will seriously affect the safety of the UAV.Based on the needs of the optimized design of the modified electro-hydrostatic braking system of the Diamond CU42 UAV,research on the short-distance braking method and the straight-line anti-bias method is carried out,and a short-distance anti-bias system that meets the requirements is designed.The main work and features are as follows:Firstly,to ensure the high-efficiency braking of UAVs in short distances,a shortdistance braking system based on optimal braking torque is proposed.The system consists of two parts: the anti-skid and anti-lock strategy and the coordinated control of the brake pressure: the anti-skid and anti-lock design can automatically identify the current runway state and use the slip coefficient τ defined by the friction coefficient model between the wheel and the runway to obtain the distance between the tire and the runway accurately.The wheel angular velocity and optimal braking torque at the friction peak position ensure that the slip braking effect of the wheel reaches the best state and shortens the braking distance.Meanwhile,a dual-loop control system of braking pressure is designed based on the current and pressure,which can achieve the precise control of the braking pressure and the rapid response requirements of the system.The closed loop braking pressure serial control method: the linear active disturbance rejection technology is used to regulate the outer pressure loop and create the control quantity（target current）of inner current loop to control the motor? for the current inner loop control,an observer bandwidth can be designed.The actual pressure to the target pressure is quickly and accurately tracked.Secondly,this study designed a joint rectification scheme in the full-speed domain for the anti-bias control aiming at the lateral deviation problem of the UAV during braking.Based on the force analysis of the UAV ground roll model,the rudder rectification method,the main wheel differential rectification method and the front wheel steering rectification method are designed using PID,fuzzy control and other methods.Then the optimization method（gradient descent method）is adopted.The three rectification methods are combined,and the rectification weight coefficients at the current sliding speed are allocated to the three rectification methods according to the gliding characteristics of the UAV at low,medium,and high speed.The aircraft glides stably along the centerline.The performance of the braking system is tested on the test platform.The results indicate that the experimental results of the anti-skid and anti-lock strategy are similar to the soft simulation results.The pressure coordination control method can realize that the braking pressure can quickly and accurately follow the target pressure.In summary,the braking system’s performance meets the design requirements and has a good short-range anti-bias effect.