An assessment of contamination pickup on ground robotic vehicles for nuclear surveying application

Ground robotic vehicles are often deployed to inspect areas where radioactive floor contamination is a prominent risk. However, the accuracy of detection could be adversely affected by enhanced radiation signal through self-contamination of the robot occurring over the course of the inspection. In this work, it was hypothesised that a six-legged robot could offer advantages over the more conventional ground robotic devices such as wheeled and tracked rovers. To investigate this, experimental contamination testing and computational Monte Carlo simulation techniques (GEANT4) were employed to understand how radioactive contamination pick-up on three different robotic vehicles would affect their detection accuracy. Two robotic vehicles were selected for comparison with the hexapod robot based on their type of locomotion; a wheeled rover and a tracked rover. With the aid of a non-toxic fluorescent tracer dust, the contamination received by the all three vehicles when traversing a contaminated area was initially compared through physical inspection using high definition cameras. The parametric results from these tests where used in the computational study carried out in GEANT4. A cadmium zinc telluride detector was simulated at heights ranging from 10 to 50 cm above each contaminated vehicle, as if it were mounted on a plinth. Assuming a uniform activity of 60 Bq cm^-2on all contaminated surfaces, the results suggested that due to the hexapod's small ground-contacting surface area and geometry, radiation detection rates using an uncollimated detector are likely to be overestimated by between only 0.07%-0.12%, compared with 3.95%-8.43% and 1.75%-14.53% for the wheeled and tracked robot alternatives, respectively.

Practical Model for Energy Consumption Analysis of Omnidirectional Mobile Robot

The four-wheeled Mecanum robot is widely used in various industries due to its maneuverability and strong load capacity, which is suitable for performing precise transportation tasks in a narrow environment. While the Mecanum wheel robot has mobility, it also consumes more energy than ordinary robots. The power consumed by the Mecanum wheel mobile robot varies enormously depending on their operating regimes and environments. Therefore, only knowing the working environment of the robot and the accurate power consumption model can we accurately predict the power consumption of the robot. In order to increase the applicable scenarios of energy consumption modeling for Mecanum wheel robots and improve the accuracy of energy consumption modeling, this paper focuses on various factors that affect the energy consumption of the Mecanum wheel robot, such as motor temperature, terrain, the center of gravity position, etc. The model is derived from the kinematic and kinetic model combined with electrical engineering and energy flow principles. The model has been simulated in MATLAB and experimentally validated with the four-wheeled Mecanum robot platform in our lab. Experimental results show that the accuracy of the model reached 95%. The results of energy consumption modeling can help robots save energy by helping them to perform rational path planning and task planning.

ADP-Based Online Tracking Control of Partially Uncertain Time-Delayed Nonlinear System and Application to Wheeled Mobile Robots

In this paper, an adaptive dynamic programming-based online adaptive tracking control algorithm is proposed to solve the tracking problem of the partial uncertain time-delayed nonlinear affine system with uncertain resistance. Using the discrete-time Hamilton-Jacobi-Bellman function, the input time-delay separation lemma, and the Lyapunov-Krasovskii functionals, the partial state and input time delay can be determined. With the approximation of the action and critic, and resistance neural networks, a near-optimal controller and appropriate adaptive laws are defined to guarantee the uniform ultimate boundedness of all signals in the target system, and the tracking error convergence to a small compact set to zero. A numerical simulation of the wheeled mobile robotic system is presented to verify the validity of the proposed method.

Design optimization of a lightweight rocker–bogie rover for ocean worlds applications

Relatively recent discoveries have shown that large quantities of water can be found on moons of some of the planets among the gas giants in our solar system. Robotic mobility systems can study the varied geology and origins of these bodies if they are able to navigate the complex terrains of ocean worlds. The topographical features of ocean worlds present a unique combination of challenges for mobility. These include cryogenic ice, penitentes, salt evaporites, chaotic regions, and regolith with uncertain shear and sinkage properties. Uncertainty in both terrain properties and geometry motivates design of a platform that is mobile within a large range of obstacle geometries and terrain properties. This article reports on a research effort to study the requirements and numerically optimize the kinematic parameters of the rover to satisfy these goals. The platforms selected in the process were further verified via simulation. A simulation and analysis of grousers generated suitable designs for interaction with similar ledges and rough terrain. From this analysis, a prototype was developed and tested to meet the wide range of topography and terramechanics conditions expected on these bodies.

Comparative Study of Different Methods in Vibration-Based Terrain Classification for Wheeled Robots with Shock Absorbers

Autonomous robots that operate in the field can enhance their security and efficiency by accurate terrain classification, which can be realized by means of robot-terrain interaction-generated vibration signals. In this paper, we explore the vibration-based terrain classification (VTC), in particular for a wheeled robot with shock absorbers. Because the vibration sensors are usually mounted on the main body of the robot, the vibration signals are dampened significantly, which results in the vibration signals collected on different terrains being more difficult to discriminate. Hence, the existing VTC methods applied to a robot with shock absorbers may degrade. The contributions are two-fold: (1) Several experiments are conducted to exhibit the performance of the existing feature-engineering and feature-learning classification methods; and (2) According to the long short-term memory (LSTM) network, we propose a one-dimensional convolutional LSTM (1DCL)-based VTC method to learn both spatial and temporal characteristics of the dampened vibration signals. The experiment results demonstrate that: (1) The feature-engineering methods, which are efficient in VTC of the robot without shock absorbers, are not so accurate in our project; meanwhile, the feature-learning methods are better choices; and (2) The 1DCL-based VTC method outperforms the conventional methods with an accuracy of 80.18%, which exceeds the second method (LSTM) by 8.23%.

Kinematics-Based Simulation and Animation of Articulated Rovers Traversing Uneven Terrains

The paper develops a simulation and animation environment for high-mobility rovers based on kinematic modeling. Various kinematic chains starting from the rover body to the wheels are analyzed and aggregated to obtain the model of the rover body motion in terms of the wheel motions. This model is then used to determine the actuations of the joints, wheels speed, and steering motors to achieve a desired motion of the rover over uneven terrain while avoiding loss of balance and tip-over. The simulation environment consists of a number of modules, including terrain and trajectory generation, and kinematic models for rover actuation and navigation. The animation of the rover motion over various terrains is developed, which allows observing the rover from various viewpoints and interacting with the system through a graphical user interface. The performance of the overall system is demonstrated by modeling a high-mobility space exploration rover, and the responses of the rover on uneven terrains are provided, which show the usefulness of the proposed modeling, simulation, and animation scheme.

The Effect of Terrain Inclination on Performance and the Stability Region of Two-Wheeled Mobile Robots

Two-wheeled mobile robots (TWMRs) have a capability of avoiding the tip-over problem on inclined terrain by adjusting the centre of mass position of the robot body. The effects of terrain inclination on the robot performance are studied to exploit this capability. Prior to the real-time implementation of position control, an estimation of the stability region of the TWMR is essential for safe operation. A numerical method to estimate the stability region is applied and the effects of inclined surfaces on the performance and stability region of the robot are investigated. The dynamics of a TWMR is modelled on a general uneven terrain and reduced for cases of inclined and horizontal flat terrain. A full state feedback (FSFB) controller is designed based on optimal gains with speed tracking on a horizontal flat terrain. The performance and stability regions are simulated for the robot on a horizontal flat and inclined terrain with the same controller. The results endorse a variation in equilibrium points and a reduction in stability region for robot motion on inclined terrain.

Continuous mobility of mobile robots with a special ability for overcoming driving failure on rough terrain

For wheeled mobile robots moving in rough terrains or uncertain environments, driving failure will be encountered when trafficability failure occurs. Continuous mobility of mobile robots with special ability for overcoming driving failure on rough terrain has rarely been considered. This study was conducted using a four-wheel-steering and four-wheel-driving mobile robot equipped with a binocular visual system. First, quasi-static force analysis is carried out to understand the effects of different driving-failure modes on the mobile robot while moving on rough terrain. Secondly, to make the best of the rest of the driving force, robot configuration transformation is employed to select the optimal configuration that can overcome the driving failure. Thirdly, sliding mode control based on back-stepping is adopted to enable the robot achieve continuous trajectory tracking with visual feedback. Finally, the efficacy of the presented approach is verified by simulations and experiments.

Coordinated control of slip ratio for wheeled mobile robots climbing loose sloped terrain

A challenging problem faced by wheeled mobile robots (WMRs) such as planetary rovers traversing loose sloped terrain is the inevitable longitudinal slip suffered by the wheels, which often leads to their deviation from the predetermined trajectory, reduced drive efficiency, and possible failures. This study investigates this problem using terramechanics analysis of the wheel-soil interaction. First, a slope-based wheel-soil interaction terramechanics model is built, and an online slip coordinated algorithm is designed based on the goal of optimal drive efficiency. An equation of state is established using the coordinated slip as the desired input and the actual slip as a state variable. To improve the robustness and adaptability of the control system, an adaptive neural network is designed. Analytical results and those of a simulation using Vortex demonstrate the significantly improved mobile performance of the WMR using the proposed control system.

Experimental study and analysis of the wheels’ steering mechanics for planetary exploration wheeled mobile robots moving on deformable terrain

Due to the requirements of challenging planetary exploration missions with wheeled mobile robots (WMRs), the driving mechanics of WMRs’ wheels moving on the deformable terrain has been researched intensively, but the mechanics of the wheels’ steering is lacking research. Systematic steering experiments were carried out using a single-wheel testbed for wheels moving on a lunar soil simulant with different radii, widths, lug heights, and lug numbers under different vertical loads. The influence of the eccentric distance and motion state, such as the steering motor’s angular velocity, steering angle, and initial wheel sinkage, were also studied. The experimental results are illustrated with plenty of figures and analyzed based on the preliminary steering mechanics model to draw conclusions. The steering resistance moment is caused by the lateral bulldoze stress and the shearing stress at the bottom of the wheel. The wheel sinkage and steering moment of resistance increase with an increase in steering angle, which could be fitted with exponential functions. The steering moment is the increasing function of the wheel sinkage, eccentric distance, vertical load, and wheel width. The conclusions, empirical models, and experimental data can be taken as references to the optimal design of a steering mechanism and the development/verification of a wheel’s steering mechanics model.

Stabilized Feedback Control of Unicycle Mobile Robots

In this paper, a stabilized feedback control is designed for a class of unicycle non-holonomic mobile robots. The approach is based on kinematic polar coordinate transformations. The suggested control scheme allows the robot to achieve stabilized near-optimal trajectories, while satisfying the hard constraints of specified initial and final postures (positions and orientations). Simulation experiments showing the effectiveness of the proposed technique are provided and discussed.

Synthesis of control law considering wheel–ground interaction and contact stability of autonomous mobile robot

We proposed a new method of mobile robot motion synthesis. A dynamical model describing the slip phenomenon taking into account the wheel–ground interaction was derived. The novelty of this work stems from the assumption that the slip already exists and the wheel motion pattern must reduce it, not exceeding the acceleration and torque limits. Moreover, a slip estimation method is proposed by introducing a critical friction coefficient. The theoretical considerations are confirmed by simulation and experiment. This research was performed in the framework of the PROTEUS project aiming at the development of autonomous robots for inspection and exploration. These robots will move in natural terrain.

Motion Analysis with Experimental Verification of the Hybrid Robot PEOPLER-II for Reversible Switch between Walk and Roll on Demand

We propose a newly renovated mobile robot PEOPLER-II (Perpendicularly Oriented Planetary Legged Robot), and addresses its motion analysis for switching its locomotion from leg-type to wheel-type and vice versa. For the leg-type locomotion, particularly in a transitional state of sitting or standing, we propose a control method based on minimization of the total energy cost using the distribution of the motor power payload in the hip and knee joints, in addition to the method of keeping the same payload factor. Also, we discuss robot configurations for switching between the two locomotion types by considering environmental factors such as walking gaits, ground inclination angle and robot’s traveling direction. Knee joint position of a pivotal foot determines knee ahead and knee behind gaits. In each switch, we check such characteristics as the hip joint rotation direction, robot center trajectory, and necessary total power in a practical point of use. Then we build three beneficial switching cycles aiming for moderate use of a motor, rider’s comfort, and power saving. Finally, we demonstrate the switching by considering the aim and verify that the results of the analysis become useful for enabling switching on demand.

Real-time model based electrical powered wheelchair control

The purpose of this study was to evaluate the effects of three different control methods on driving speed variation and wheel slip of an electric-powered wheelchair (EPW). A kinematic model as well as 3D dynamic model was developed to control the velocity and traction of the wheelchair. A smart wheelchair platform was designed and built with a computerized controller and encoders to record wheel speeds and to detect the slip. A model based, a proportional-integral-derivative (PID) and an open-loop controller were applied with the EPW driving on four different surfaces at three specified speeds. The speed errors, variation, rise time, settling time and slip coefficient were calculated and compared for a speed step-response input. Experimental results showed that model based control performed best on all surfaces across the speeds.