Slip And Path Tracking Control Of The Deep Sea Tracked Miner

Abstract:Due to its particular structural feature, tracked vehicles are widely used in military, agricultural and mining applications. For the deep sea mining task, mining research using a tracked miner system has been conducted in many countries. As an indispensable subsystem of the whole deep sea mining system, the operating motion control of the tracked miner is becoming a research focus.Because the tracked mine goes on the extremely cohesive sediment, the traction force is provided by shear stress which is caused by the shear displacement of the track. Because of inherent soil mechanics of the sediment, slippage under the track will be produced when the miner walks on the soil, and the change of the slip rate will affect the dynamic behavior of the miner. Since the working path of the miner is planned ahead, the trajectory of tracked miner in the real working condition can hardly go with the desired path. To ensure mining productivity, path tracking serves as one of the critical operating motion control. To guarantee the stability of the whole integrated deep sea mining system, follower control between the miner and the ship is also of great essence. In this paper, these three motion control problems are concerned and proper control strategies and algorithms are proposed. After a series of simulation tests and experiments, the feasibility and validity of the algorithms has been confirmed.The main research achievements are as follows:1. Based on the terrain mechanics of the tracked vehicle, a calculation formula, which reflects the relationship both the pressure and sinkage as well as the shear stress and shear displacement, is established. Also the relationship between the traction force and the slippage is set up.By analysis of the motion resistance, a thorough dynamic and kinetic model of the tracked miner is established. To avail the research, a simplified dynamic model is proposed and the error coming along is analyzed. From the theoretical respect, all these work facilitates the motion control of the miner.2. According to the relationship between the traction force and slippage, judging criteria of optimal slippage, which based on homogeneous soil, is put forward; also a method to identify the optimal slippage under non-homogeneous soil is established. To better control of slippage of the miner, a fuzzy PID control strategy and a model of slip control system is developed. By a series of simulation under both homogeneous and non-homogeneous soil condition, the effectiveness and stability of the strategy is testified.3. The difficulty of the path tracking control is described and the deviation model of the path tracking of the miner is developed. By taking the dynamic constrain of the miner, the smoothness of the trajectory and the time-optimal method into consideration, a time-optimal control strategy, which is based on the cubic spline curve, is proposed. Via Lyapunov method, the stability of the algorithm has been proven. For the instability situations resulting from the deploying process of the miner, the corresponding control tactics are developed. Also, the model of the path tracking control system is established. By analysis of the simulation results, the optimum coefficient, which value is0.66, is determined. After a series of tracking simulation under straight path, circular path and actual mining path, the validity of this control strategy is testified. Comparing with the PID control algorithm, it turns out that the proposed algorithm has a better time-optimal feature.4. According to the total system design for the1000m sea trial project, two operating paths are contrasted, which are longitudinal and transverse. A distance of240m between the miner and the ship is chosen as the objectives for the integrated motion control of the whole system. Then a series of simulation both under fair current and counter current has been done. From the result of the simulation, the strategy can satisfy the control requirement.5. A series of experiments concerning the critical motion control have been conducted. In the experiments, mixture of the bentonite and the water is used as the simulated sediment. By measuring the mechanical property under different ratio of bentonite and the water, the optimal ratio is determined, that is1.5:1. According to the results from six group traction-slippage tests, the theoretical derivation method is verified. Through path tracking experiments, it indicates that the testing miner can moving along the desired path accurately, thus the correctness and the credibility of the simulations of path tracking can be verified.