Jianguo Tao

Interaction Mechanics Model for Rigid Driving Wheels of Planetary Rovers Moving on Sandy Terrain with Consideration of Multiple Physical Effects

Predicting wheel-terrain interaction with semiempirical models is of substantial importance for developing planetary wheeled mobile robots rovers. Primarily geared toward the design of manned terrestrial vehicles, conventional terramechanics models do not provide the sufficient fidelity required for application on autonomous planetary rovers. To develop a high-fidelity interaction mechanics model, in this study the physical effects of wheel lug, slip sinkage, wheel dimension, and load are analyzed based on experimental results, including wheel sinkage, drawbar pull, normal force, and moment, which are measured on a single-wheel test bed. The mechanism of lug-terrain interaction is investigated systematically to clarify the principle of increasing shear stress, conditions of forming successive shearing among adjacent lugs, and the influence on shear displacement of soil. A mathematical model for predicting the concentrated forces and torque of rigid wheels with lugs for planetary rovers moving on sandy terrain is derived by integrating the improved models of normal and shearing stress distributions. In addition to the wheel parameters, terrain parameters, and motion state variables, wheel-terrain interaction parameters, such as the linear varying sinkage exponent, the soil displacement radius, and load effect parameters, were proposed and explicitly included in the model. In the single-wheel experiments, the slip ratio was increased approximately from 0.05 to 0.6, and the relative errors of the predicted results using the proposed model are less than 10% for all the wheels when compared with the experimental data. The proposed model has been used in the simulation of a four-wheeled rover, and its effectiveness is evaluated by comparing the simulation results with experimental results.

Adaptive Sliding Mode Control of Mobile Manipulators with Markovian Switching Joints

The hybrid joints of manipulators can be switched to either active (actuated) or passive (underactuated) mode as needed. Consider the property of hybrid joints, the system switches stochastically between active and passive systems, and the dynamics of the jump system cannot stay on each trajectory errors region of subsystems forever; therefore, it is difficult to determine whether the closed-loop system is stochastically stable. In this paper, we consider stochastic stability and sliding mode control for mobile manipulators using stochastic jumps switching joints. Adaptive parameter techniques are adopted to cope with the effect of Markovian switching and nonlinear dynamics uncertainty and follow the desired trajectory for wheeled mobile manipulators. The resulting closed-loop system is bounded in probability and the effect due to the external disturbance on the tracking errors can be attenuated to any preassigned level. It has been shown that the adaptive control problem for the Markovian jump nonlinear systems is solvable if a set of coupled linear matrix inequalities (LMIs) have solutions. Finally, a numerical example is given to show the potential of the proposed techniques.

Adding Sub-chain Method for Structural Synthesis of Planar Closed Kinematic Chains

For at least the past five decades, structural synthesis has been used as a main means of finding better mechanisms with some predefined function. In structural synthesis, isomorphism identification is still a problem unsolved well, and to solve this problem is very significant to the design of new mechanisms. According to the given degree of freedom (DOF) and link connection property of planar closed chain mechanisms, vertex assortment is obtained. For solving the isomorphism problem, a method of the adding sub-chains is proposed with the detailed steps and algorithms in the synthesizing process. Employing this method, the identification code and formation code of every topological structure are achieved, therefore many isomorphic structures could be eliminated in time during structural synthesis by comparing those codes among different topological graphs, resulting in the improvement of synthesizing efficiency and accuracy, and the approach for eliminating rigid sub-chains in and after the synthesizing process is also presented. Some examples are given, including how to add sub-chains, how to detect simple rigid sub-chains and how to obtain identification codes and formulation codes et al. Using the adding sub-chain method, the relative information of some common topological graphs is given in the form of table. The comparison result is coincident with many literatures, so the correctness of the adding sub-chain method is convinced. This method will greatly improve the synthesizing efficiency and accuracy, and has a good potential for application.

Effect of Slip on Tractive Performance of Small Rigid Wheel on Loose Sand

For obtaining the optimal range of wheel slip for driving control and simulation of planetary rover, the experiments were conducted to analyze the effect of slip on tractive performance of different diameter and width rigid wheel in loose sand bin. All the tests were done at a free wheel sinkage in a single-wheel test bed. By the comparison of tractive performance between smooth wheel and the wheel with different straight grousers, drawbar pull and torque are observed to increase with slip up to a maximum value which is approached asymptotically, it indicates that the optimal range of slip is from 10% to 45% for driving control which is dependent on the behavior of sand. Through applying the tracive performance index to the experimental results, the preferable value of wheel slip is deduced to be 13% for the similar sand used in the experiment from the prospect of saving energy.

Development of a Wheeled Robotic Rover in Rough Terrains

Robotic rovers are mobile robots to perform challenging tasks in unstructured terrain. In this paper a six-wheeled robotic rover was developed with mobility in rough terrain. The rover consists of three configuration segments with a pair of cylinder-conical motorized wheels, joined together by two articulated suspensions with three degree-of-freedom. The two articulated suspensions will improve the rover mobility maneuver in different terrains by passive or active suspension configurations. Different locomotion modes of the rover are discussed based on terrain conditions, and some simulations about those models are shown. A control system of the rover based on combination of teleoperation and autonomous locomotion is described. Some experiments testify the rover excellent mobility in rough terrains and strong obstacle-overcoming capability

Research on Wheel-walking Motion Control of Lunar Rover with Six Cylinder-conical Wheels

Motion control of a lunar rover is precondition of accomplishing exploration tasks. In order to minimize the power consumption, the power optimum control was carried out for a lunar rover prototype with six cylinder-conical wheels in wheel-walking motion mode. In terms of mechanism principle and configuration features of the lunar rover, the kinematics model of wheel-walking motion was built up. The optimum control model of the motion mode was derived by applying minimal value principle, and the simulation model was constituted based on Simulink. The simulation analysis was carried out. The research results illustrate the validity of optimum control model of wheel-walking motion. The paper gives theory basis for designing motion control system and drive system optimization of lunar rover.

Kinematic modeling of a six-wheeled robotic rover with a passive/active suspension

A six-wheeled robotic rover with passive/active suspensions was designed considering the uneven terrain. The rover suspension consists of two 3-DOF articulated frames, and each joint of the suspensions can rotate passively or be driven by a motor. So the rover is capable of locomotion in a passive mode or an active mode according to terrain. Based on the rover mechanical characteristics, reference frames for describing the rover locomotion are set up and a closed chain coordinate transformation graph is given. A kinematics modeling method of the rover for passive locomotion mode and active locomotion mode is presented. Kinematics models of the rover in passive locomotion mode and wheel-walking locomotion mode on rough terrain are constructed considering some key factors such as terrain characteristics, joint movement of suspensions, wheel slippage and so on. Some calculation results show validity of the kinematics models of the rover.

Mechanical Analysis and Measurement of Parameters of Wheel -Soil Interaction for a Lunar Rover

Mechanical models of the wheel-soil interaction are constructed for a rigid wheel of lunar rover when rolling and steering, based on the theories of terramechanics and passive earth pressure. The mechanical affect of different parameters of the soil to the rigid wheel is analysed, such as drawbar pull, rolling torque and steering torque. Experimental results of a rigid wheel in a kind of dry soil, whose mechanical parameters are some similar to lunar soil, validate the models correct. A novel test-bed and its data acquisition system are also designed for testing the performance of the wheel-soil interaction of lunar rover, and their key technologies concerned are discussed.

Twisting door handles and pulling open doors with a mobile manipulator

The ability of twisting door handles and opening doors is essential for modern robots to work in non-industrial environment. In this paper, two basic problems are addressed: the selection of the inverse kinematics solution and the generation of the path during the process. An algorithm is proposed to find the appropriate solution of the IK problem. In the proposed algorithm, the continuity and periodicity of joint angles are considered and the final solution is selected by minimizing the Euclidean distance from the current state. The path is generated under the kinematics constraints of the door and the limitation of the work space of the manipulator. The experiments are carried out on a real robot with a 6DoF manipulator and a mobile platform. The experimental results showed that the robot system was able to twisting door handles and pull open doors which also proved the correctness of the proposed algorithm and the path generating method.

Interact with robot: An efficient approach based on finite state machine and mouse gesture recognition

Communication between human operators and robots is important. In this paper, two problems are addressed: (1) how a robot can change its behavior sequences in manipulation tasks with human intervention; (2) how a human operator can transfer information to a robot efficiently. We tackle the first problem by proposing a framework based on finite state machine to model the robot action sequences in manipulation tasks. The framework shows the way in which a robot slides its level of autonomy by considering the result of the transition action and the input of the human operator. The framework can be easily extended to include higher level of autonomy. To tackle the second problem, we proposed a method to encode human intentions into simple mouse gestures. With a discriminative classifier, the robot can recognize the mouse gesture drawn by the human operator and carry out the corresponding action. The classifier is based on PCA and has been tested on our data set collected from four volunteers with an average precision of 96.25%.