A portable six-wheeled mobile robot with reconfigurable body and self-adaptable obstacle-climbing mechanisms

Mobile robots can replace rescuers in rescue and detection missions in complex and unstructured environments and draw the interest of many researchers. This paper presents a novel six-wheeled mobile robot with a reconfigurable body and self-adaptable obstacle-climbing mechanisms, which can reconfigure itself to three locomotion states to realize the advantages of terrain adaptability, obstacle crossing ability and portability. Design criteria and mechanical design of the proposed mobile robot are firstly presented, based on which the geometry of the robot is modelled and the geometric constraint, static conditions and motion stability condition for obstacle crossing of the robot are derived and formulated. Numerical simulations are then conducted to verify the geometric passing capability, static passing capability and motion stability and find feasible structure parameters of the robot in obstacle crossing. Further, a physical prototype of the proposed mobile robot is developed and integrated with mechatronic systems and remote control. Using the prototype, field experiments are carried out to verify the feasibility of the proposed design and theoretical derivations. The results show that the proposed mobile robot satisfies all the criteria set and is feasible for applications in disastrous rescuing scenarios.

Study on the Motion Stability of the Autonomous Underwater Helicopter

The hydrodynamic performance of a novel hovering autonomous underwater vehicle, the autonomous underwater helicopter (AUH), with an original disk-shaped hull (HG1) and an improved fore–aft asymmetric hull (HG3), is investigated by means of computational fluid dynamics with the adoption of overlapping mesh method. The hydrodynamic performance of the two hull shapes in surge motion with variation of the angle of attack is compared. The results show that HG3 has less resistance and higher motion stability compared to HG1. With the angle of attack reaching 10 degrees, both HG1 and HG3 achieve the maximum lift-to-drag ratio, which is higher for HG3 compared to HG1. Furthermore, based on the numerical simulation of the plane motion mechanism test (PMM) and according to Routh’s stability criterion, the horizontal movement and vertical movement stability indexes of HG1 and HG3 (GHHG1=1.0, GVHG1=49.7, GHHG2=1.0, GVHG3=2.1) are obtained, which further show that the AUH has better vertical movement stability than the torpedo-shaped AUV. Furthermore, the scale model tail velocity experiment indirectly shows that HG3 has better hydrodynamic performance than HG1.

Design and analysis of a six-wheeled companion robot with mechanical obstacle-overcoming adaptivity

A six-wheeled companion exploration robot with an adaptive climbing mechanism is proposed and released for the complicated terrain environment of planetary exploration. Benefiting from its three-rocker-arm structure, the robot can adapt to complex terrain with its six wheels in contact with the ground during locomotion, which improves the stability of the robot. When the robot moves on the flat ground, it moves forward through the rotation of the wheels. When it encounters obstacles in the process of moving forward, the front obstacle-crossing wheels hold the obstacle, and the rocker arms on both sides rotate themselves with mechanical adaptivity to drive the robot to climb and cross the obstacle like crab legs. Furthermore, a parameterized geometric model is established to analyze the motion stability and the obstacle-crossing performance of the robot. To investigate the feasibility and correctness of design theory and robot scheme, a group of design parameters of the robot are determined. A prototype of the robot is developed, and the experiment results show that the robot can maintain stability in rugged terrain environments and has a certain ability to surmount obstacles.

Subregional Process Method With Variable Parameters Based on a Potential Field in Slow Tool Servo Machining for a Complex Curved Surface

Precision turning with slow tool servo (STS) plays an increasingly important role in advanced manufacturing nowadays. However, it is difficult to promote machining quality for surfaces with local complex geometric features by the conventional global machining method. Hence, a subregional processing method in STS is proposed. First, the continuous equipotential line is taken to express the local geometric feature. Thus, a potential field is built, where the surface could be divided into subregions. Then, a subregional toolpath with variable feed rates is generated by the field and stitched to ensure the feeding motion stability of X-axis. Finally, the surface is subdivided for variable spindle speed planning, considering the feeding motion stability of Z-axis. It is found that the profile arithmetic average error reduces by 31.58% with the proposed method compared with that with the conventional method and the machining time is shortened by 41.00%. Thus, it is proved that the new processing method effectively promotes machining quality and efficiency.

The stability analysis using Lyapunov exponents for high-DOF nonlinear vehicle plane motion

The Lyapunov exponents method is an excellent approach for analyzing the vehicle plane motion stability, and the researchers demonstrated the effectiveness under 2-DOF vehicle model. However, whether the Lyapunov exponents approach can effectively reveal the characteristics of high-DOF nonlinear vehicle model is the key problem at present. In this paper, the Lyapunov exponents is applied to quantitatively analyze the stability of the nonlinear three and five degree of freedom vehicle plane motion system. The different characteristics between 2-DOF and high-DOF model are revealed and explained by using Lyapunov exponents. It illustrates the feasibility of using Lyapunov exponents to analyze the stability of high-DOF vehicle models, which supplements and perfects the existing quantitative analysis conclusion.

Compliant Detachment of Wall-Climbing Robot Unaffected by Adhesion State

Adhesion state is a key factor affecting the motion stability of a wall-climbing robot. According to different adhesion states, there is no universal method for compliant detachment. We propose an online impedance strategy for controlling peeling angle to realize compliant movement. Variable compliant motions are achieved by online tuning the stiffness and damping parameters of proportional-derivative control, which realizes compliant detachment with a peeling angle of π, the adhesion strength to adjust to a minimum and basically eliminated the instant change in normal adhesion strength at the detachment end state. The proposed controller was validated using a vertical climbing robot. The results showed that, with the proposed controller, the sudden change in the normal adhesion force during peeling was significantly reduced. Besides, there is no correlation between the sudden change in the normal adhesion force at the detachment end state and the adhesion state. Regardless of the adhesion states, the compliant detachment can be accomplished reliably.