A comprehensive method for joint wear prediction in planar mechanical systems with clearances considering complex contact conditions

A comprehensive method to predict wear in planar mechanical systems with clearance joints is presented and discussed in this paper.This method consists of a system dynamic analysis and a joint wear prediction.As the size and shape of the clearance are dictated by wear and evolve with the dynamic response of the system,the contact between the journal and bearing could be conformal or non-conformal,which makes the contact conditions in clearance joints quite complicated.Therefore a modified contact force model is employed to evaluate the joint reaction force in this study.As the nonlinear stiffness coefficient is related to the physical and geometrical properties of contact bodies and varies with the deformation,this contact force model is applicable to different contact conditions between the journal and bearing.Furthermore,based on the Archard’s wear model,the amount of wear can be quantified in the joint.And the geometry is updated to reflect the evolving contact boundary.Then,the wear process and the contact force model are integrated into the motion equations of the system to perform coupled iterative analyses between system dynamic response and joint wear prediction.In addition,a slider-crank mechanism is simulated as an example to demonstrate efficiency of the proposed method and to carry out a parametric study on mechanical systems considering joint wear.The influence of clearance size and driving power are discussed and compared respectively.The index of concordance is introduced to quantify contributions of contact pressure and sliding distance to wear rate under different types of journal motion.This study could help to predict joint wear in mechanical systems with clearances and optimize mechanisms in design.     

Design, analysis and control for an antarctic modular manipulator

Antarctic scientific expedition has important strategic significance. It is an inevitable trend to apply robots to assist researchers during the Antarctic expedition. However, the robot manipula- tors at present have a series of problems and unable to meet the requirements of the Antarctic expe- dition. In this paper, a novel Antarctic modular robot manipulator is proposed, which has a compact structure with modular joints. The robot manipulator has high reliability, and quick assembling-and- disassembling ability. Through well wires arranging and thermal controlling, the manipulator can better adapt to the Antarctic environment. In addition, the work space of the manipulator is serious- ly analyzed, and a new hybrid position/force control method is adopted to make the manipulator per- form better. Simulation results validate the control method and show that the robot manipulator has a good performance to meet the requirements of Antarctic expedition.     

Probabilistic analysis of random contact force between geomembrane and granular material

A probabilistic method based on principle of maximum entropy was employed to analyze the randomness of contact force between geomembrane and granular material. The contact force distribution is exponential according to the proposed method and the grain size is the most important factor that affects the distribution of contact force. The proposed method is then verified by a series of laboratory experiments using glass beads and cobbles as granular material and a very thin pressure, indicating that film is firstly used in these experiments which give a reliable method to measure the contact force at each contact point.     

Robot motion control in mobile environment

With the problem of robot motion control in dynamic environment represented by mobile obstacles, working pieces and external mechanisms considered, a relevant control actions design procedure has been proposed to provide coordination of robot motions with respect to the moving external objects so that an extension of robot spatial motion techniques and active robotic strategies based on approaches of nonlinear control theory can be achieved.     

Linearizing the soft finger contact constraint with application to dynamic force distribution in multifingered grasping

Multifingered grasping was ardently studied in the past two decades. Force-closureproperty and dynamic force distribution (DFD) are two basic topics. The former ensuresthat the contact forces of a grasp can equilibrate any external wrench. The latter seeksthe optimal contact forces to equilibrate a dynamic external wrench. Force-closure is aprerequisite to stable grasps, while fast force distribution is required for real-time controlof dexterous robot hands. There are three common conta…     

Force Based Skill Learning for Robot Tasks in Contact Conditions

To acquire human operation skill based on force sense, element contact form (ECF) is proposed to describe contact-condition firstly. The skill is modeled as a sequence of discrete ECFs. Since different ECF has different force distribution, a support vector machine classifier is built to identify the contact conditions according to the force signal. Finally, the robot can obtain the skill from the human demonstration.     

Dynamic Analysis and Structural Optimization of a Novel Palletizing Robot

A novel palletizing robot is presented and developed.By using the Newton-Euler method and the principle that the instantaneous inertial force system could be transformed into a static system,the force equilibrium equations of the whole robot and its subsystem were derived and the robot’s dynamic models were established.After that,an example simulation was performed by using Matlab software and the structural optimization of the robot’s key parts were discussed and analyzed in ANSYS platform.The results show that the dynamic models are correct and can be helpful for the design,validation and kinetic control based on dynamics of this kind of palletizing robots.     

Building of cognizing semantic map in large-scale semi-unknown environment

The quick response code based artificial labels are applied to provide semantic concepts and relations of surroundings that permit the understanding of complexity and limitations of semantic recognition and scene only with robot＇s vision. By imitating spatial cognizing mechanism of human, the robot constantly received the information of artificial labels at cognitive-guide points in a wide range of structured environment to achieve the perception of the environment and robot navigation, The immune network algorithm was used to form the environmental awareness mechanism with ＂distributed representation＂. The color recognition and SIFT feature matching algorithm were fused to achieve the memory and cognition of scenario tag. Then the cognition-guide-action based cognizing semantic map was built. Along with the continuously abundant map, the robot did no longer need to rely on the artificial label, and it could plan path and navigate freely. Experimental results show that the artificial label designed in this work can improve the cognitive ability of the robot, navigate the robot in the case of semi-unknown environment, and build the cognizing semantic map favorably.     

Adhesion forces for water/oil droplet and bubble on coking coal surfaces with different roughness

Surface roughness plays a significant role in floatability of coal. In the present paper, coking coal surface was polished by three different sandpapers and the surface properties were characterized by contact angle and roughness measurements. The effect of surface roughness on floatability was investigated by adhesion force measurement system for measuring interaction forces between droplets/bubbles and coking coal surfaces with different roughness. The results showed that the contact angle decreased with increasing roughness yet the adhesion force between the water droplet and coal surface increased owing to the increased contact line and the appearance of line pinning. Maximum adhesion forces between water and surfaces were 111.70, 125.48, and 136.42 μN when the roughness was 0.23, 0.98, and 2.79 μm, respectively. In contrast, under a liquid environment, the adhesion forces between air bubble/oil droplet and coal surfaces were decreased with increasing roughness because of the restriction by water. Maximum adhesion forces of increasing roughness were 97.14, 42.76, and 17.86 μN measured at interfaces between air bubble and coal surfaces and 169.48, 145.84, and 121.02 μN between oil droplet and surfaces, respectively. Decreasing roughness could be beneficial to the spreading of oil droplets and the adhesion of bubbles which is conducive to flotation separation.     

Cartesian impedance control of dexterous robot hand

Presents a novel compliant motion control for a robot hand using the Cartesian impedance approach based on fingertip force measurements. The fingertip can accurately track desired motion in free space and appear as mechanical impedance in constrained space. In the position based impedance control strategy, any switching mode in contact transition phase is not needed. The impedance parameters can be adjusted in a certain range according to various tasks. In this paper, the analysis of the finger‘s kinematics and dynamics is given. Experimental results have shown the effectiveness of this control strategy.     

Immune evolutionary algorithms with domain knowledge for simultaneous localization and mapping

1 INTRODUCTIONSi multaneous localization and mapping(SLAM) or concurrent mapping and localizationcan be described as follows :acquiring a map of anunknown environment with a moving robot , andsi multaneously localizing the robot relative to thismap[1 2]. The SLAMproblemaddresses situationswhere the robot lacks a global positioning sensor ,andinsteadit has to rely on sensors of incrementalego-motion for robot position esti mation (e .g.odometry ,inertial navigation,etc .) .Such sensorsa…     

Joint space compliance control for a hydraulic quadruped robot based on force feedback

In the realm of quadruped robot locomotion, compliance control is imperative to handle impacts when negotiating unstructured terrains. At the same time, kinematic tracking accuracy should be guaranteed during locomotion. To meet both demands, a joint space compliance controller is designed, so that compliance can be achieved in stance phase while position tracking performance can be guaranteed in swing phase. Unlike operational space compliance control, the joint space compliance control method is easy to implement and does not depend on robot dynamics. As for each joint actuator, high performance force control is of great importance for compliance design. Therefore, a nonlinear PI controller based on feedback linearization is proposed for the hydraulic actuator force control. Besides, an outer position loop(compliance loop) is closed for each joint. Experiments are carried out to verify the force controller and compliance of the hydraulic actuator. The robot leg compliance is assessed by a virtual prototyping simulation.     

Modelling and simulation of contact force in cold rotary forgin简

Cold rotary forging is an advanced and complex metal forming technology with continuous local plastic deformation. Investigating the contact force between the dies and the workpiece has a great significance to improve the life of the dies in cold rotary forging. The purpose of this work is to reveal the contact force responses in cold rotary forging through the modelling and simulation. For this purpose, a 3D elastic-plastic dynamic explicit FE model of cold rotary forging is developed using the FE code ABAQUS/Explicit. Through the modelling and simulation, the distribution and evolution of the contact force in cold rotary forging is investigated in detail. The experiment has been conducted and the validity of the 3D FE model of cold rotary forging has been verified. The results show that： 1） The contact force distribution is complex and exhibits an obvious non-uniform characteristic in the radial and circumferential directions; 2） The maximum contact force between the upper die and the workpiece is much larger than that between the lower die and the workpiece; 3） The contact force evolution history is periodic and every period experiences three different stages; 4） The total normal contact force is much larger than the total shear contact force at any given time.     

Mobile robot path planning based on adaptive bacterial foraging algorithm

The utilization of biomimicry of bacterial foraging strategy was considered to develop an adaptive control strategy for mobile robot, and a bacterial foraging approach was proposed for robot path planning. In the proposed model, robot that mimics the behavior of bacteria is able to determine an optimal collision-free path between a start and a target point in the environment surrounded by obstacles. In the simulation, two test scenarios of static environment with different number obstacles were adopted to evaluate the performance of the proposed method. Simulation results show that the robot which reflects the bacterial foraging behavior can adapt to complex environments in the planned trajectories with both satisfactory accuracy and stability.     

Traveling property of wheel-type pipeline robot with different configurations

In order to improve the travelling ability of the wheel-type pipeline robot in elbow section of pipeline,the model of drive ratios is proposed aiming at the pipeline robots with different configurations.Through the movement analysis of the robot with different configurations in elbow section,the pose model of the robot is established,and the coordinates of the wheel centers and the contact points can be got through the calculation of the pose model.Based on the pose model established,the corresponding drive ratios are obtained combining with the relations of the velocities of wheel centers and rotative velocities of wheels under the movement condition with no interference.The virtual simulations and prototype experiments are carried out,and the drive ratios accuracy of the model when the robot moved in elbow without interference is validated.     

Impacts of flexible obstructive working environment on dynamic performances of inspection robot for power transmission line

The rigid-flexible coupling dynamic modeling and simulation of an inspection robot were conducted to study the influences of the flexible obstructive working environment i.e. overhead transmission line on the robot＇s dynamic performance. First, considering the structure of the obstacles and symmetrical mechanism of the robot prototype, four basic subactions were abstracted to fulfill full-path kinematic tasks. Then, a multi-rigid-body dynamic model of the robot was built with Lagrange equation, whil~e a multi-flexible-body dynamic model of a span of lin~ was obtained by combining finite element method （FEM）, modal synthesis method and Lagrange equation. The two subsystem models were coupled under rolling along no-obstacle segment and overcoming obstacle poses, and these simulations of three subactions along different spans of line were performed in ADMAS. The simulation results, including the coupling vibration parameters and driving moment of joint motors, show the dynamic performances of the robot along ftexibile obstructive working path： in flexible obstructive working environment, the robot can fulfill the preset motion goals; it responses slower in more flexible path; the fluctuation of robot as well as driving moment of the corresponding joint in startup and brake region is greater than that in rigid environment; the fluctuation amplitude increases with increasing working environment flexibility.     

Hybrid force control of astronaut rehabilitative training robot under active loading mode

In order to mitigate the effects of space adaptation syndrome(SAS) and improve the training efficiency of the astronauts, a novel astronaut rehabilitative training robot(ART) was proposed. ART can help the astronauts to carry out the bench press training in the microgravity environment. Firstly, a dynamic model of cable driven unit(CDU) was established whose accuracy was verified through the model identification. Secondly, to improve the accuracy and the speed of the active loading, an active loading hybrid force controller was proposed on the basis of the dynamic model of the CDU. Finally, the actual effect of the hybrid force controller was tested by simulations and experiments. The results suggest that the hybrid force controller can significantly improve the precision and the dynamic performance of the active loading with the maximum phase lag of the active loading being 9° and the maximum amplitude error being 2% at the frequency range of 10 Hz. The controller can meet the design requirements.     

An analysis method for correlation between catenary irregularities and pantograph-catenary contact force

Pantograph-catenary contact force provides the main basis for evaluation of current quality collection; however, the pantograph-catenary contact force is largely affected by the catenary irregularities. To analyze the correlated relationship between catenary irregularities and pantograph-catenary contact force, a method based on nonlinear auto-regressive with exogenous input （NARX） neural networks was developed. First, to collect the test data of catenary irregularities and contact force, the pantograph/catenary dynamics model was established and dynamic simulation was conducted using MATLAB/Simulink. Second, catenary irregularities were used as the input to NARX neural network and the contact force was determined as output of the NARX neural network, in which the neural network was trained by an improved training mechanism based on the regularization algorithm. The simulation results show that the testing error and correlation coefficient are 0.1100 and 0.8029, respectively, and the prediction accuracy is satisfactory. And the comparisons with other algorithms indicate the validity and superiority of the proposed approach.     

A reconfigurable tracked mobile robot based on four-linkage mechanism

A novel reconfigurable tracked robot based on four-link mechanism was proposed and released for the complicated terrain environment. This robot was modularly designed and developed, which is composed of one suspension and one pair of symmetrical deployed reconfigurable track modules. This robot can implement multiple locomotion configurations by changing the track configuration, and the geometric theory analysis shows that the track length keeps constant during the process of track reconfiguration. Furthermore, a parameterized geometric model of the robot was established to analyze the kinematic performance of the robot while overcoming various obstacles. To investigate the feasibility and correctness of design theory and robot scheme, an example robot was designed to climb 45° slopes and 200 mm steps, and a group of design parameters of the robot were determined. Finally, A prototype of this robot was developed, and the test results show that the robot own powerful mobility and obstacle overcoming performance, for example, running across obstacle like mantis, extending to stride over entrenchment, standing up to elevate height, and going ahead after overturn.     

An object tracking and global localization method using the cylindrical projection of omnidirectional image

We present an omnidirectional vision system we have implemented to provide our mobile robot with a fast tracking and robust localization capability. An algorithm is proposed to do reconstruction of the environment from the omnidirectional image and global localization of the robot in the context of the Middle Size League RoboCup field. This is accomplished by learning a set of visual landmarks such as the goals and the comer posts.Due to the dynamic changing environment and the partially observable landmarks, four localization cases are discussed in order to get robust localization performance. Localization is performed using a method that matches the observed landmarks, i.e. color blobs, which are extracted from the environment. The advantages of the cylindrical projection are discussed giving special consideration to the characteristics of the visual landmark and the meaning of the blob extraction. The analysis is established based on real time experiments with our omnidirectional vision system and the actual mobile robot. The comparative studies are presented and the feasibility of the method is shown.