Hyper-redundant Robot Research Articles

Design of a torsional stiffener for a cable-driven hyper-redundant robot composed of gear transmission joints

AbstractThis work describes the advancement in developing a cable-driven gear transmission joint designed as a basic element for a long-reach hyper-redundant robot. Hyper-redundancy allows the robot to perform auxiliary tasks such as obstacle avoidance and joint limits satisfaction. This feature makes hyper-redundant robots particularly useful for performing tasks in confined and hazardous environments and areas that are not reachable by a human operator. The long-reach feature of the robot requires a detailed study of the overall structure and its components. The joint must be capable of transmitting forces and movements over a long distance without losing the precision and accuracy of the end-effector, so it is designed to optimise the robot’s performance in terms of stiffness, structural resistance, and functional characteristics. In light of the above considerations, the main focus of this work is to improve the structural performance of the entire robotic system. Consequently, since the most critical component of the robot in terms of torsional deformation is the gear transmission joint, this paper aims to design a torsional stiffener element to reduce its deformation and, thus, an increase of torsional stiffness of the overall robotic system. Tube-shaped and rectangular-shaped stiffener elements, which can fit the joint design satisfying its geometrical constraints, are proposed. A computer-aided engineering approach is implemented to improve the precision of positioning of the end-effector by adding stiffener elements in the joint. Two sensitivity analyses, varying the geometry of the proposed stiffener elements, are performed to evaluate their performance in terms of added mass and displacement reduction.

A Bidirectional Human-Machine Control Interface Based on Virtual Fixtures for Safe Teleoperation of Hyper-Redundant Robots

A Bidirectional Human-Machine Control Interface Based on Virtual Fixtures for Safe Teleoperation of Hyper-Redundant Robots

Shape-controllable inverse kinematics of hyper-redundant robots based on the improved FABRIK method

AbstractHyper-redundant robots have good prospects for applications in confined space due to their high flexibility and slim body size. However, the super-redundant structure brings great challenges for its inverse kinematics with shape constraints. Unfortunately, traditional Jacobian pseudo-inverse-based inverse kinematics method and forward and backward reaching inverse kinematics (FABRIK) method are difficult to constrain the arm shape and realize trajectory tracking in confined spaces. To solve this problem, we propose a shape-controllable FABRIK method to satisfy the given path and shape constraints. Firstly, the kinematic model of the hyper-redundant robot is established, and the canonical FABRIK method is introduced. Based on the preliminary works, the single-layer improved FABRIK method is developed to solve the position and pointing inverse kinematics considering path environment and joint angle constraints instead of two-layer geometric iterations. For tracking the desired end roll angles, the polygonal virtual arm is designed. The real arm roll angle is achieved by controlling its winding on the virtual arm. In this way, the shape can be controlled. Finally, we compare the proposed method with other three approaches by simulations. Results show that the proposed method is more efficient and the arm shape is controllable.

Dual-Loop Control of Cable-Driven Snake-like Robots

Snake-like robots, which have high degrees of freedom and flexibility, can effectively perform an obstacle avoidance motion in a narrow and unstructured space to complete assignments efficiently. However, accurate closed-loop control is difficult to achieve. On the one hand, this is because adding too many sensors to the robot will significantly increase its mass, size, and cost. On the other hand, the more complex structure of the hyper-redundant robot also challenges the more elaborate closed-loop control strategy. For these reasons, a cable-driven snake-like robot, which is compact and low cost, with force transducers and angle sensors, is designed in this article. The simpler and more direct kinematic model is studied, which applies to a widely used kinematics algorithm. Based on the kinematic model, the inverse dynamics are resolved. Finally, this article analyzes the sources of the motion errors and achieves dual-loop control through force-feedback and pose-feedback. The experiment results show that the robot’s structure and dual-loop control strategy function with high accuracy and reliability, meeting the requirements of engineering applications and high-precision control.

Dexterous obstacle-avoidance motion control of Rope Driven Snake Manipulator based on the bionic path following

The RDSM (Rope Driven Snake Manipulator) is a hyper-redundant robot operating in narrow and confined environments, such as aerospace, nuclear industry and etc. Inspired from the bionic following motion, an obstacle-avoidance control method of the RDSM in uncharted environments is proposed without the information of global obstacles. First, the kinematic model of a 17-DOF RDSM is established considering the mapping among the joint angle, rope length and end posture. Then, the motion path and inverse kinematic iterative algorithm of the RDSM in multi-obstacle environments is deduced using the piecewise Bézier curves. The motion control method of the RDSM is designed based on the model reference adaptive control, guaranteeing the joint error and end posture error asymptotically stable. Finally, the proposed obstacle avoidance method is verified with the simulation and experiment. As the result shown, the RDSM avoids obstacles on a path with a minimum curvature radius of 1/8 arm length, and the motion control precision of the end posture is within ±2.5mm/±0.5∘.

Magnetic Ball Chain Robots for Endoluminal Interventions.

This paper introduces a novel class of hyperredundant robots comprised of chains of permanently magnetized spheres enclosed in a cylindrical polymer skin. With their shape controlled using an externally-applied magnetic field, the spherical joints of these robots enable them to bend to very small radii of curvature. These robots can be used as steerable tips for endoluminal instruments. A kinematic model is derived based on minimizing magnetic and elastic potential energy. Simulation is used to demonstrate the enhanced steerability of these robots in comparison to magnetic soft continuum robots designed using either distributed or lumped magnetic material. Experiments are included to validate the model and to demonstrate the steering capability of ball chain robots in bifurcating channels.

Design and development of a cable-driven elephant trunk robot with variable cross-sections

PurposeIn large equipment and highly complex confined workspaces, the maintenance is usually carried out by snake-arm robots with equal cross-sections. However, the equal cross-sectional design results in the snake arm suffering from stress concentration and restricted working space. The purpose of this paper is to design a variable cross-section elephant trunk robot (ETR) that can address these shortcomings through bionic principles.Design/methodology/approachThis paper proposes a cable-driven ETR to explore the advantages and inspiration of variable cross-section features for hyper-redundant robot design. For the kinematic characteristics, the influence of the variable cross-section design on the maximum joint angle of the ETR is analysed using the control variables method and the structural parameters are selected. Based on the biological inspiration of the whole elephant trunk following the movement of the trunk tip, a trajectory-tracking algorithm is designed to solve the inverse kinematics of the ETR.FindingsSimulation and test results show the unique advantages of the proposed variable cross-section ETR in kinematics and forces, which can reduce stress concentrations and increase the flexibility of movement.Originality/valueThis paper presents a design method for a variable cross-section ETR for confined working spaces, analyses the kinematic characteristics and develops a targeted trajectory control algorithm.

A dexterous motion control method of rope driven snake manipulator considering the rope-hole properties

The RDSM (rope driven snake manipulator) is a hyper redundant robot operating in narrow and confined space. However, the rope-hole properties of the mechanism are ignored mostly, resulting in the significant trajectory tracking error of the RDSM. To solve the problem, a RDSM prototype with 16 DOFs is designed firstly. Then the rope-hole nonlinear model is established considering the friction, clearance and rope flexibility. Based on the rope-hole nonlinear model, the rope length is corrected, and the kinematic model of the RDSM without considering the rope-hole properties is improved. The joint state observer and trajectory tracking controller of the RDSM are designed using the improved kinematic model. Finally, the proposed kinematic model and controller of the RDSM are verified by the virtual prototype and experimental prototype. The results show that the control precision of the RDSM can be improved significantly with the rope-hole compensation. The end position error is improved from the level of cm to mm, and the end attitude error is improved by about 60%.

Trajectory Optimization Methods of a Space Hyper-redundant Robot Based on Effective Arm-Shape Measurement

Trajectory Optimization Methods of a Space Hyper-redundant Robot Based on Effective Arm-Shape Measurement

Dizajn pid kontrolera frakcionog reda za kontrolu praćenja putanje kontinualnih robota

Continuum robots are the behavioral extension of hyper-redundant robots usually inspired by living biological organs. These robots outperform their rigid counterparts regarding high flexibility, dexterity, and most importantly safe interaction. On the flip side, they are kinematically redundant, highly nonlinear, and multi-input, and consequently, their controlling remains a complex and challenging task. To this end, this paper proposes a Fractional-Order Proportional-Integral-Derivative (FOPID) controller to control the continuum robot's end-tip. The proposed controller is designed to control the inputs of a class of continuum robots, namely the Cable-Driven Continuum Robot (CDCR). To design the controller satisfactorily, the Particle Swarm Optimization (PSO) algorithm extracts the optimal values of the controller's parameters. The proposed FOPID controller's efficiency and control performance are demonstrated through two simulation examples: set-point tracking and point-to-point trajectory tracking. In addition, the obtained simulation results are compared to those provided by classical and Optimized PID controllers and to some available schemes. Given the obtained results, it is clear that the performances of the proposed FOPID controller are superior in tracking accuracy and smoothness in control signals.

The development of AUV control system with accommodation to thruster faults

Abstract A new method for the synthesis of AUV control system for high-precision and highly reliable spatial motion is proposed. The feature of these control systems is that they include an additional accommodation circuit that provides timely detection, determination of the magnitude and compensation for the consequences of the appearance of minor faults that occur in the AUV thrusters. The simulation results confirmed the efficiency and high quality of the synthesized systems. Key words Dynamics modeling of system of solids, unmanned underwater vehicle, UUV, AUUV, mobile robot, hyper-redundant robot, computer design of machines and mechanisms, SolidWorks Motion, MCS.ADAMS. Acknowledgements This work was supported by the Russian Foundation for Basic Research (projects 20-38-70161 and 19-08-00347).

Simulation of the motion dynamics of a modular unmanned underwater vehicle during reconfiguration in a liquid medium

Abstract For the previously proposed design of a modular underwater robot, a solid-state model of an unmanned underwater vehicle (UUV) with the possibility of changing the shape of the streamlined body during operation in a liquid environment has been developed. A technique for constructing assembly nodes in 3D CAD is proposed, which allows automating the determination of the position of the rigid node’s pressure center. For the assembly developed in the SolidWorks package and retrofitted in the SolidWorks Motion Add-on with models of drives and external influences and environment, modeling of the behavior dynamics of the system of solids in a liquid viscous medium for fixed configurations of the UUV and transients during transformation from one configuration to another was performed. Estimates of the coordinates of the center of mass and the center of pressure of the UUV in various configurations are obtained. Recommendations for refining the model have been developed. The article was prepared on the basis of the report at the 32nd International Conference Extreme Robotics [5] on the recommendation of the Conference Organizing Committee. Key words Dynamics modeling of system of solids, unmanned underwater vehicle, UUV, AUUV, mobile robot, hyper-redundant robot, computer design of machines and mechanisms, SolidWorks Motion, MCS.ADAMS. Acknowledgements The work was performed in the framework of the state task of the Ministry of Education and Science of the Russian Federation no. 075-00913-21-01.

Numerical Shape Planning Algorithm for Hyper-Redundant Robots Based on Discrete Bézier Curve Fitting

The paper proposes a novel numerical method S-GUIDE that provides real-time planning of the shape of hyper-redundant robots with serial architecture by means of a guidance curve, represented in parametrized analytical form and in numerical form by a set of key points associated with the robot structure. To model the shape of the robot, the method uses an equivalent model, and a shape guidance curve obtained through a controlled adjustment of a Bézier curve. This is achieved in three computing steps were the robot equivalent structure, it’s associated kinematic parameters and the robot actuation parameters in joint space are calculated. The proposed method offers several advantages in relation with the precision, computing time and the feasibility for real-time applications. In the paper, the method accuracy, execution time, and the absolute error for different work scenarios are determined, compared and validated.

Axis manipulation to solve Inverse Kinematics of Hyper-Redundant Robot in 3D Space

A solution based on inverse kinematics is required for the robot's end effector, also known as its tip, to reach a target. Current methods for solving the inverse kinematics solution for a hyper-redundant robot in three 3D are generally complex, difficult to visualize, and time-intensive. This requires the development of new algorithms for solving inverse kinematics in a quicker and more efficient manner. In this study, an axis manipulation using a geometrical approach is used. Initially, a general algorithm for a 2 m-link hyper-redundant robot in 3D is generated. The method employed a repetitive basic inverse kinematics solution of a two-link robot on virtual links. The virtual links are generated using a specific geometric proposition. Finally, the 3D solution is generated by rotating about the global z-axis. This method reduces the mathematical complexity required to solve the inverse kinematics solution for a 2-m-link robot. In addition, this method can manage variable link manipulators, thereby eliminating singularity. To demonstrate the effectiveness of the model, numerical simulations of hyper redundant models in 3D are presented. This new geometric approach is anticipated to enhance the performance of hyper-redundant robots, enabling them to be of greater assistance in fields such as medicine, the military, and search and rescue.

Kinematic Modelling for Hyper-Redundant Robots—A Structured Guide

Obtaining mathematical equations to model the kinematics of a hyper-redundant robot is not intuitive and of greater difficulty than for traditional robots. Depending on the characteristics of the robot, the most appropriate methodology to approach the modelling may be one or another. This article provides a general overview of the different approaches there are when modelling a hyper-redundant cable-driven robot, while proposing a guide to help the novel researcher that approaches this field decide which methodology to apply when modelling a robot. After providing some definitions, a simple framework to understand all the underlying models is presented. Afterwards, the mathematical equations for the most important methods of modelling are developed. Finally, the proposal for a step-by-step tutorial is included, and it is exemplified by applying it to three real robots.

Operational Space Iterative Learning Control of Coupled Active/Passive Multilink Cable-Driven Hyper-Redundant Robots

Abstract The operational space control (OSC) of multilink cable-driven hyper-redundant robots (MCDHRs) is required to perform tasks in many applications. As a new coupled active-passive (CAP) MCDHR system, due to the multiple couplings between the active cables, the passive cables, the joints, and the end-effector, the OSC becomes more and more complicated. However, there is currently no robust and effective control method to solve the OSC problem of such types MCDHRs. In this paper, an OSC framework of CAP-MCDHRs using a dynamics-based iterative-learning-control (ILC) method is proposed, considering multivariate optimization. First, the multi-coupling kinematics and the series-parallel coupling dynamics equation (i.e., cable-joint-end) of the CAP-MCDHR are derived. Then, a dynamics-based trajectory tracking framework was constructed. Moreover, an OSC accuracy evaluation model based on a high-precision laser tracker was also designed. The framework allows the tracking of operational space trajectories (OSTs) online with the feasible cable tension and the joint angle. It is also shown that the tracking performance can be improved through the ILC when the desired trajectory is repeatedly performed. Finally, a simulation and an experimental hardware system are built. The results show that the proposed control framework can be easily and effectively applied to the CAP-MCDHR used in real-time.

An Accurate Position Acquisition Method of a Hyper-Redundant Arm With Load

The constant curvature model is the most widely used kinematics model of hyper-redundant robots. However, it incurs large errors when the robots have load or large deformation. To address these issues, this paper proposes a position acquisition method with combination of the flexible sensors and the kinematics model. A hyper-elastic sensor based on the liquid alloy is developed to directly test the geometric parameters of the robot joints. The mapping model between the resistance and the length of the flexible sensor is also built. By combining with the kinematics model and the testing data of flexible sensors, the overall position of the hyper-redundant arm can be calculated. To verify the position acquisition method, a three joints hyper-redundant arm is built to test the coordinates with non-load and load conditions. The experiment results show the correctness of the method, and it can be extended to various types of hyper-redundant robots.

Design of a Novel Long-Reach Cable-Driven Hyper-Redundant Snake-like Manipulator for Inspection and Maintenance

Robotic inspection and maintenance are gaining importance due to the number of different scenarios in which robots can operate. The use of robotic systems to accomplish such tasks has deep implications in terms of safety for human workers and can significantly extend the life of infrastructures and industrial facilities. In this context, long-reach cable-driven hyper-redundant robots can be employed to inspect areas that are difficult to reach and hazardous environments such as tanks and vessels. This paper presents a novel long-reach cable-driven hyper-redundant robot called SLIM (Snake-Like manipulator for Inspection and Maintenance). SLIM consists of a robotic arm, a pan and tilt mechanism as end-effector, and an actuation box that can rotate and around which the arm can wrap. The robot has a total of 15 degrees of freedom and, therefore, for the task of positioning the tool centre point in a bi-dimensional Cartesian space with a specific attitude, it has 10 degrees of redundancy. The robot is designed to operate in harsh environments and high temperatures and can deploy itself up to about 4.8 m. This paper presents the requirements that drove the design of the robot, the main aspects of the mechanical and electronic systems, the control strategy, and the results of preliminary experimental tests performed with a physical prototype to evaluate the robot performances.

Adaptive trajectory control of an under-actuated snake robot

This article proposes an adaptive trajectory control method for under-actuated snake robots by simplifying the control and actuation systems of hyper-redundant robots. The under-actuated joints are formed by controlling the spatial rotation angles of multiple rigid joints in the joint group in order for them to synchronize. Based on the under-actuated configuration, a trajectory control algorithm is proposed and includes the following parts: (i) A control principle based on variable rod length is adopted so that the snake robot can track into a small working space; (ii) a trajectory planning of the snake robot in a fixed state at one end is realized by an iterative tractrix principle minimizing the joint displacement; and (iii) a fast return tracking control of the snake robot in any posture is realized by adopting the principles of the variable rod-length tractrix and the forced return iteration. A snake robot with an arm 2300 mm in length is designed and fabricated. The trajectory control simulation and experiments validate the correctness of the trajectory control algorithm and the rationality of the structural design.

Path Planning Based on NURBS for Hyper-Redundant Manipulator Used in Narrow Space

Hyper-redundant manipulators with multiple degrees of freedom have special application prospects in narrow spaces, such as detection in small spaces in aerospace, rescue on-site disaster relief, etc. In order to solve the problems of complex obstacle avoidance planning and inverse solution selection of a hyper-redundant robot in a narrow space, a cubic B-spline curve based on collision-free trajectory using environmental edge information is planned. Firstly, a hyper-redundant robot composed of four pairs of double UCR (Universal-Cylindrical-Revolute) parallel mechanisms (2R1T, 2 Rotational DOFs and 1 Translation DOF) in series to realize flexible obstacle avoidance motion in narrow space is designed. The trajectory point envelope of a single UCR and the workspace of a single pair of UCR in Cartesian space based on the motion constraint boundaries of each joint are obtained. Then, the constraint control points according to the edge information of the obstacle are obtained, and the obstacle avoidance trajectory in the constrained space is planned by combining the A* algorithm and cubic B-spline algorithm. Finally, a variety of test scenarios are built to verify the obstacle avoidance planning algorithm. The results show that the proposed algorithm reduces the computational complexity of the obstacle avoidance process and enables the robot to complete flexible obstacle avoidance movement in the complex narrow space.