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.

Effect of submerged body shape upon its movement pattern near free surface

Object and purpose of research. This paper discusses the tests with submerged models of different shape moving near the free surface in the test tank. The purpose of the study was to determine how relative vertical displacement and crosssection shape lift of submerged body depend on the speed of its movement at different immersion depths. Materials and methods. Model test procedure, techniques and results of model. Numerical simulation was performed in ANSYS software package. Main results. Experimental and theoretical study on cross-section shape effect of submerged body upon its wave generation, vertical lift and movement pattern near free surface. Conclusion. The results of this research will be useful for further work towards greater horizontal movement stability of submerged body at various speeds depending on its hull shape and immersion depth.

Investigation of Vehicle Stability with Consideration of Suspension Performance

The issue of movement stability remains highly relevant considering increasing vehicle speeds. The evaluation of vehicle stability parameters and the modeling of specific movement modes is a complex task, as no universal evaluation criteria have been established. The main task in modeling car stability is an integrated assessment of the vehicle’s road interactions and identification of relationships. The main system affecting the vehicle’s road interaction is the suspension of the vehicle. Vehicle suspension is required to provide constant wheel to road surface contact, thus creating the preconditions for stability of vehicle movement. At the same time, it must provide the maximum possible body insulation against the effect of unevennesses on the road surface. Combining the two marginal prerequisites is challenging, and the issue has not been definitively solved to this day. Inaccurate alignment of the suspension and damping characteristics of the vehicle suspension impairs the stability of the vehicle, and passengers feel discomfort due to increased vibrations of the vehicle body. As a result, the driving speed is artificially restricted, the durability of the vehicle body is reduced, and the transported cargo is affected. In the study, analytical computational and experimental research methods were used. Specialized vehicle-road interaction assessment programs were developed for theoretical investigation. The methodology developed for assessing vehicle movement stability may be used for the following purposes: design and improvement of vehicle suspension and other mechanisms that determine vehicle stability; analysis of road spans assigned with characteristic vehicle movement settings; road accident situation analysis; design of road structures and establishment of certain operational restrictions on the road structures. A vehicle suspension test bench that included original structure mechanisms that simulate the effect of the road surface was designed and manufactured to test the results of theoretical calculations describing the work of the vehicle suspension and to study various suspension parameters. Experimental investigations were carried out by examining the vibrations of vehicle suspension elements caused by unevenness on the road surface.

Mechanism Design and Experiment of a Bionic Turtle Dredging Robot

In order to clean underwater silt in artificially constructed rivers, lakes, and fish ponds, for which no suitable tool exists, a tool has been developed that imitates the structure and movement of the tortoise’s legs, and designs a four-legged dredging robot that can adapt to the complex underwater environment. The article uses the transformation matrix to analyze the kinematics of the dredging robot, determines the movement sequence of the outriggers according to the principle of stability, and analyzes the movement characteristics of the three gait modes. Then, we combined the control function of the foot trajectory with the experimental prototype based on the bionic tortoise mechanism to carry out a walking experiment. During the experiment, the motion stability is good. Additionally, the changes in the position, the posture of the outriggers, and the body prove that the movement stability of the dredging robot using coordinated gait, mixed gait, and intermittent gait has increased sequentially.

Adaptive Virtual Impedance Control of a Mobile Multi-Robot System

The capabilities of collaborative robotics have transcended the conventional abilities of decentralised robots as it provides benefits such as scalability, flexibility and robustness. Collaborative robots can operate safely in complex human environments without being restricted by the safety cages or barriers that often accompany them. Collaborative robots can be used for various applications such as machine tending, packaging, process tasks and pick and place. This paper proposes an improvement of the current virtual impedance algorithm by developing an adaptive virtual impedance controlled mobile multi-robot system focused on dynamic obstacle avoidance with a controlled planar movement. The study includes the development of a mobile multi-robot platform whereby each robot plans a path individually without a supervisor. The proposed system would implement a two-layered hierarchy for robot path planning. The higher layer generates a trajectory from the current position to the desired position, and the lower layer develops a real-time strategy to follow the generated trajectory while avoiding static and dynamic obstacles. The key contribution of this paper is the adaptive virtual impedance controller for a multi-robot system that will maintain movement stability and improve the motion behaviour in a dynamic environment.

Trajectory planning of the nursing robot based on the center of gravity for aluminum alloy structure

In this paper, the robot arm is manufactured to increase the structural strength and improve safety. The stability of the nursing robot in the process of carrying out the typical nursing task of holding patients was studied, and the influence of the center of gravity on the movement stability of the nursing robot was analyzed. The mathematical model of the stability of the robot is built by using the inverse kinematics solution of the robot. By studying the trajectory planning of a nursing robot under the condition of ZMP constraint, the robot can move safely and optimally along the prescribed trajectory between two working points. The simulation results show that the algorithm can significantly improve the work safety of the robot. In the experiment, four pressure sensors are used to measure the pressure of four wheels on the ground, the data are obtained and substituted into the expression of center of pressure (COP) method. The results show that the stability is in a reasonable moving area without any hidden danger, and its COP value is less than the stable qualitative boundary, which verifies the rationality and effectiveness of the optimal center of gravity stability planning algorithm.

MOVEMENT STABILITY OF A SECTION OF THE MACHINE FOR BLACK FALLOW CULTIVATION IN A LONGITUDINAL-VERTICAL PLANE

One of the tasks of using the black fallow in agricultural production is the weed control and the moisture conservation in the soil. Application of the most advanced soil cultivation technologies ensures preservation of no more than 75% of precipitations in the soil. To improve the state of this issue, we have developed a special machine for processing the black fallow. A mathematical model has been developed that describes the dynamics of the movement of the harrow section in a longitudinal-vertical plane, and its solution is given, which allows investigation of the impact of this or that design parameter upon the dynamics of the angle of rotation in time. The adequacy of the developed mathematical model is confirmed by special laboratory and field investigations of the created experimental machine. With rational design parameters the rotation angle of the harrow section in a longitudinal-vertical plane will not exceed – 3º, and the time of its exit to the equilibrium position will not exceed 16...17 s.

Joint Trajectory Planning of Space Modular Reconfigurable Satellites Based on Kinematic Model

This paper investigates the application of particle swarm optimization (PSO) algorithm to plan joint trajectories of the space modular reconfigurable satellite (SMRS). SMRS changes its configuration by joint motions to complete various space missions; its movement stability is affected by joints motions because of the dynamic coupling effect in space. To improve the movement stability in reconfiguration progress, this paper establishes the optimization object equation to characterize the movement stability of SMRS in its reconfiguration process. The velocity-level and position-level kinematic models based on the proposed virtual joint coordinate system of SMRS are derived. The virtual joint coordinate system solves the problem of asymmetric joint coordinate system resulted by the asymmetric joint arrangement of SMRS. The six-order and seven-order polynomial curves are chosen to parameterize the joint trajectories and ensure the continuous position, velocity, and acceleration of joint motions. Finally, PSO algorithm is used to optimize the trajectory parameters in two cases. Consistent optimization results in terms of the six-order and seven-order polynomial in both cases prove the PSO algorithm can be effectively used for joint trajectory planning of SMRS.

Overturning and rolling avoidance by gecko when challenged with inclines

Understanding how animals avoid overturning and rolling in motion to maintain movement stability and to accommodate their habitat and the mechanisms of movement in these habitats is a matter of concern. Gecko climbs a more inclined substrate by lowering the speed; meanwhile, the duty factor is increased with the increase of the incline angle, indicating that the gecko switches the diagonal gait when climbing on the shallow inclines to the triangular gait when on the inverted surface. The overturning impulse moment is increased with an increase of the incline angle. On inclines larger than 90°, the positive and negative overturning impulse moments are increased significantly and show obvious differences. The maximum value of rolling impulse moment on the surface at 180° can reach 15 times that of the minimum value on the surface at 90°, and the positive and negative rolling impulse moments at the inclined surface of 120–180° have obvious differences. The above results show that on shallow inclines, the low centre of mass and the flat posture of the gecko can effectively improve locomotion stability; simultaneously, through the timely conversion of the limb function, the overturning/rolling impulse moments are low, which greatly reduces the probability of overturning/rolling during locomotion. However, on inverted inclines, the gecko takes full advantage of the flexibility of body and limbs to delay the occurrence of rolling and overturning, and actively cooperates with the adjustment of the gait, using the alternating change of gait to avoid overturning and rolling.