Hyper-redundant Manipulator Research Articles

Design and Kinematic Control of the Cable-Driven Hyper-Redundant Manipulator for Potential Underwater Applications

Underwater manipulators are important robotic tools in the exploration of the ocean environment. Up to now, most existing underwater manipulators are rigid and with fixed 5 or 7 degrees of freedom (DOF), which may not be very suitable for some complicated underwater scenarios (e.g., pipe networks, narrow deep cavities, etc.). The biomimetic concept of muscles and tendons is also considered as continuum manipulators, but load capacity and operation accuracy are their essential drawbacks and thus limit their practical applications. Recently, the cable-driven technique has been developed for manipulators, which can include numerous joints and hyper-redundant DOF to execute tasks with dexterity and adaptability and thus they have strong potential for these complex underwater applications. In this paper, the design of a novel cable-driven hyper-redundant manipulator (CDHRM) is introduced, which is driven by multiple cables passing through the tubular structure from the base to the end-effector, and the joint numbers can be extended and decided by the specific underwater task requirements. The kinematic analysis of the proposed CDHRM is given which includes two parts: the cable-joint kinematics and the joint-end kinematics. The geometric relationship between the cable length and the joint angles are derived via the established geometric model for the cable-joint kinematics, and the projection relationship between the joint angles and end-effector’s pose is established via the spatial coordinate transformation matrix for the joint-end kinematics. Thus, the complex mapping relationships among the cables, joints and end-effectors are clearly achieved. To implement precise control, the kinematic control scheme is developed for the CDHRM with series-parallel connections and hyper-redundancy to achieve good tracking performance. The experiment on a real CDHRM system with five joints is carried out and the results verify the accuracy of kinematics solution, and the effectiveness of the proposed control design. Particularly, three experiments are tested in the underwater environment, which verifies its good tracking performance, load carrying and grasping capacity.

Reachable workspace determination for a spatial hyper-redundant manipulator formed by several parallel manipulators

Solving the reachable workspaces of spatial hyper-redundant manipulators (SHRMs) formed by serially connected parallel manipulators is an important and challenging work. This study addresses the issue on reachable workspaces and establishes a novel CAD-VBbased workspace determination system for determining the reachable workspaces of SHRMs. The reachable workspace determination of a novel (3-RPS)+(3-SPR)+(3-RPS) SHRM, a triple delta-type SHRM, and a novel (3-RRS)+(3-SPR)+(3-RRS) SHRM shows the generality and effectiveness of the proposed approach. The system proposed in this study can contribute to reachable workspace analysis for SHRMs.

A Hybrid Obstacle-Avoidance Method of Spatial Hyper-Redundant Manipulators for Servicing in Confined Space

SummaryDue to a large number of redundant degrees of freedom (DOFs), the hyper-redundant manipulator shows outstanding dexterity and adaptability in avoiding the obstacles in confined space. In this paper, a hybrid obstacle-avoidance method of spatial hyper-redundant manipulators is proposed, with both efficiency and accuracy considered. The space around an obstacle is classified into safe, warning, and dangerous zones. A two-level protection strategy is then addressed to handle the obstacle-avoidance problem from qualitative (i.e., pseudo-distance based on super-quadric function) and quantitative (i.e., Euclidean distance based on practical geometry function) perspectives, respectively. The only condition for switching between the two-level protections is the value of pseudo-distance. Then, a modified modal method, which is a trajectory planning method, is presented to plan the collision-free trajectory of the manipulator by maximizing the minimum pseudo-distance or Euclidean distance in different zones. Some parameters, including the arm-angle parameters and the equivalent link length parameters, are defined to represent the manipulator configuration. They are adjusted to avoid the obstacle, singularity, and joint limit. The simulations of 12-DOF manipulator and an experiment of 18-DOF manipulator verify the proposed methods.

Simultaneous Planning Method Considering Both Overall Configuration and End Pose for Hyper-Redundant Manipulators

Featured by extreme flexibility, hyper-redundant manipulators are gradually developed and applied to perform detection and maintenance tasks in confined on-orbit environments. However, its configuration planning is very challenging due to a large number of degrees of freedom. This paper proposes a simultaneous planning method considering both overall configuration and end pose for hyper-redundant manipulators. First, the end effector and intermediate universal joints of the hyper-redundant manipulator are selected as the follow-up controlled points. The corresponding active control points are freely set near the follow-up controlled points. Then, the Euclidean distance between the active control point and the follow-up controlled point is calculated. Combined with gradient projection method, the calculated Euclidean distance is taken as the objective function to be optimized. By adjusting the active control point and the scale factor of gradient projection method, the adjustment of follow-up controlled points (i.e. overall configuration and end pose) can be realized. What is more, this method can optimize its overall configuration to adjust the follow-up controlled points close to or far from the active control point to achieve other planning goals (i.e. obstacle avoidance, singularity avoidance and so on). Therefore, this method satisfies the requirements of simultaneous planning considering both overall configuration and end pose for hyper-redundant manipulators. Finally, the proposed simultaneous planning method is executed in physical experiment system. Results verify the effectiveness of the proposed method.

有关节约束超冗余机械臂的增益优化轨迹规划

有关节约束超冗余机械臂的增益优化轨迹规划

Stiffness Control for Soft Surgical Manipulators

Tunable stiffness control is critical for undertaking surgical procedures using soft manipulators. However, active stiffness control in soft continuum manipulators is very challenging and has been rarely realized for real-time surgical applications. Low stiffness at the tip is much preferred for safe navigation of the robot in restricted spaces inside the human body. On the other hand, high stiffness at the tip is demanded for efficiently operating surgical instruments. In this paper, the manipulability and characteristics of a class of soft hyper-redundant manipulator, fabricated using Ecoflex-0050[Formula: see text] silicone, is discussed and a new methodology is introduced to actively tune the stiffness matrix, in real-time, for disturbance rejection and stiffness control. Experimental results are used to derive a more accurate description of the characteristics of the soft manipulator, capture the varying stiffness effects of the actuated arm and consequently offer a more accurate response using closed loop feedback control in real-time. The novel results presented in this paper advances the state-of-the-art of tunable stiffness control in soft continuum manipulators for real-time applications.

An improved artificial potential field method of trajectory planning and obstacle avoidance for redundant manipulators

In this article, we present an improved artificial potential field method of trajectory planning and obstacle avoidance for redundant manipulators. Specifically, we not only focused on the position for the manipulator end-effectors but also considered their posture in the course of trajectory planning and obstacle avoidance. We introduced boundaries for Cartesian space components to optimize the attractive field function. Moreover, the manipulator achieved a reasonable speed to move to the target pose, regardless of the difference between the initial pose and target pose. We proved the stability using Lyapunov stability theory by introducing velocity feedforward, when the manipulator moved along a continuous trajectory. Considering the shape of the manipulator joints and obstacles, we set up the collision detection model by projecting the obstacles to link coordinates. In this case, establishing the repulsive field between the nearest points on every joint and obstacles with the closest distance was sufficient for achieving obstacle avoidance for redundant manipulators. The simulation results based on a nine-degree-of-freedom hyper-redundant manipulator, which was designed and made in our laboratory, fully substantiated the efficacy and superiority of the proposed method.

Dynamic feedforward control of spatial cable-driven hyper-redundant manipulators for on-orbit servicing

SUMMARYThe hyper-redundant manipulators are suitable for working in the constrained on-orbit servicing environment due to the extreme flexibility. However, its modelling and control are very challenging due to the characteristics of non-linearity and strong coupling. In this paper, considering the multi-level mapping among the motors, cables, joints, and end-effector, a proportional derivative (PD) with dynamic feedforward compensation control system is designed. The corresponding control system is divided into five parts: controller, planner, actuator, manipulator, and sensor. The actual control torque consisting of the desired feedforward torque and the feedback torque is generated by the controller. In order to improve the tracking accuracy and maintain rapid response, the torque, which is calculated by the dynamics model of the traditional joint-driven manipulator, is regarded as the desired feedforward torque. The parameters of interest are the angle and velocity of the universal joint and motors. The planner plans and converts the desired parameters of the universal joint to corresponding motors. Combining with the feedback angles and velocities signals of the corresponding motors, the feedback torque can be calculated by the PD control module. Finally, typical cases of six universal joints (12DOFs) manipulators are simulated and experimented. The results demonstrate that the method is very efficient for controlling spatial cable-driven hyper-redundant manipulators.

Kinematics, Dynamics, and Control of a Cable-Driven Hyper-Redundant Manipulator

A cable-driven hyper-redundant manipulator has superior dexterity for confined space applications. However, the modeling and control considering the cables are very complex. In this paper, we established the kinematics and dynamics models and proposed a dynamics control strategy. The multilevel mapping between the motors, cables, joints, and end-effector was first analyzed. The corresponding kinematics equations were derived and solved by combining analytical and numerical methods. Especially, the cable coupling relationship was established and a decoupling method was addressed to compensate the coupled motion between cables. Furthermore, we derived the dynamics equations including the cable forces and the joint variables. Considering practical control requirements, the cables' forces were distributed by simplifying the dynamics equations and obtaining the minimal solutions. Then, we presented a dynamics control strategy, which uses the forward and inverse kinematics of multilevel mapping for motion resolution and compensation, and computes the feedforward torques for the motors using recursive dynamics and “cable force-motor torque” relationship. Finally, a prototype and a truss inspection experiment system were developed to verify the corresponding models and methods. Experiment results show that the derived kinematic and the dynamic equations, and the proposed dynamic control strategy are effective.

Continuous Path Planning of Kinematically Redundant Manipulator using Particle Swarm Optimization

This paper addresses a problem of a continuous path planning of a redundant manipulator where an end-effector needs to follow a desired path. Based on a geometrical analysis, feasible postures of a self-motion are mapped into an interval so that there will be an angle domain boundary and a redundancy resolution to track the desired path lies within this boundary. To choose a best solution among many possible solutions, meta-heuristic optimizations, namely, a Genetic Algorithm (GA), a Particle Swarm Optimization (PSO), and a Grey Wolf Optimizer (GWO) will be employed with an optimization objective to minimize a joint angle travelling distance. To achieve n-connectivity of sampling points, the angle domain trajectories are modelled using a sinusoidal function generated inside the angle domain boundary. A complex geometrical path obtained from Bezier and algebraic curves are used as the traced path that should be followed by a 3-Degree of Freedom (DOF) arm robot manipulator and a hyper-redundant manipulator. The path from the PSO yields better results than that of the GA and GWO.

ALGORITHM OF EULER-LAGRANGE METHOD FOR DEISGNING OF DYNAMIC MODEL

Urgency of the research. Nowadays robotics and mechatronics come to be mainstream. With development in these areas also grow computing fastidiousness. Since there is significant focus on numerical modeling and algorithmization in kinematic and dynamic modeling. Target setting. By automation of whole process of dynamic model design the errors are eliminated as well as the time of designing significantly decreases. Actual scientific researches and issues analysis. Designing of dynamic model by analytical way is very difficult especially in the cases considering high number of DOF. For hyperredundant manipulators it is practically impossible. From this reason whole process is automatized. Uninvestigated parts of general matters defining. The theory of Euler – Lagrange method is automatized by means of robotic view on this issue. The research objective. In the paper, an algorithm for design of dynamic model was introduced. The statement of basic materials. The paper deals with automatic design process of dynamic model for serial kinematic structure mechanisms. In the paper Euler – Lagrange formula is discussed. Analytical way of dynamic modeling should be difficult problem especially for mechanisms with high number of degrees of freedom. From this reason the paper shows the way of automatically designing of dynamic modeling in MATLAB. Our study shows dependence of computing time on increasing DOF. The relation is expressed by function of 3rd order. Subsequently the paper presents automatically generated inverse dynamic model in cooperation with inverse kinematic model as well as trajectory planning task. Conclusions. The paper introduces automatically generated dynamic model for mechanisms with serial kinematic structure. The paper also established the time for designing of dynamic model for several mechanisms with changing DOF.

ANALYSIS OF AIR-SPRING FOR A LINK OF HYPER-REDUNDANT MANIPULATOR

Urgency of the research. This research paper deals with a designing and analyzing of link for hyper-redundant manipulator/mechanism. The paper investigates 6-DOF manipulator link, consisting of pneumatic as well as electromagnetic actuators. A motion of upper platform of the link is reached by pneumatic actuators, namely air-springs. The main focus of this research is analysis of air-spring and its properties. From this reason FEM analysis is done in software SolidWorks. In the conclusion the results are discussed. Pneumatic actuators can play interesting role in order to be possible to change the mechanical properties of the manipulators. Target setting. Analysis of air-spring actuator for hyper-redundant manipulator. Actual scientific researches and issues analysis. Most of robotic arms consist of electrical actuators. Using pneumatic actuators the manipulator gets new properties like changing stiffness. Uninvestigated parts of general matters defining. Air-springs are still in the process of investigation from the view of mechanisms actuator. The research objective. In the paper simulations and analysis of the air-spring are done. The statement of basic materials. This paper investigates the area of modeling in software SolidWorks. At first CAD model of new segment for hyperredundant manipulator is introduced and its basic parts are described. Then, in the preprocessing phase, the detailed steps of its setup SolidWorks computation core were described. The second half of the article is to focus on the calculation and assessment of simulation results. Conclusions. The paper introduces new kind of manipulator link. The link is analyzed and tested by simulation.

Tip-following Path Planning and Its Performance Analysis for Hyper-redundant Manipulators

Tip-following Path Planning and Its Performance Analysis for Hyper-redundant Manipulators

Time-optimal trajectory planning for hyper-redundant manipulators in 3D workspaces

Abstract A novel approach is proposed for time-optimal trajectory planning of a hyper-redundant manipulator which is requested to move from an initial configuration to a final configuration in 3D workspaces. The 3D workspace is cluttered with static objects which have known geometry and position. The proposed approach generates a trajectory for the manipulator's end-effector considering simultaneously the kinematical constraints of the manipulator (specifically velocity and acceleration) and the presence of obstacles. The method solves an optimization problem to find the minimum time trajectory to perform the requested tasks. The optimization problem is solved by using a Genetic Algorithm with multiple population. The efficiency of the developed method is investigated and discussed through characteristic simulated experiments concerning a variety of operating environments.

A fast converging optimal technique applied to path planning of hyper-redundant manipulators

A multi-pass sequential localized search technique to solve the problem of path planning of hyper-redundant manipulators for the shortest path in real-time in the presence of obstacles is proposed. The problem is approached from a control perspective as a shortest path optimal control problem, where the configuration space is searched for path points that optimize a cost function. This method addresses the “curse of dimensionality” of exhaustive search techniques via a multi-pass sequential localized search, and sensitivity to local minima of greedy approaches via a backtracking technique. Further, theoretical proof shows that the proposed technique converges to a global optimal (if only one exists) or a suboptimal (if many exist) solution. The algorithm is implemented on a 6-DOF PUMA 560 and a 9-DOF hyper-redundant manipulator arm and simulation results are analyzed for cost and time of execution.

An algorithm for defining the inner geometry of a snakelike manipulator in case of leading link movements along the incremental trajectory

In the paper, we have formulated the invariant description form for geometry of a spatial, kinematically redundant manipulator with the orthogonal non-coplanar axes of rotation of the joints. We have obtained the explicit equations for determining the angular coordinates from the condition that points of joints belong to the smooth parametrically given curve. Inequality constraints on the relative position of neighboring parts of the manipulator have been formulated. We have proposed an algorithm for solving equations and the method of planning changes for hinge coordinates for the movement of joints points along the spatial curve that is formed by incremental addition of target points for the head link positions of the manipulator. The method has been applied for planning movements of a hyper-redundant manipulator with a fixed root link and a snakelike robot when moving along the path built on the basis of current and forecasted positions of joints in the Cartesian space.

A Fibonacci control system with application to hyper-redundant manipulators

We study a model for snake-like robots based on the Fibonacci sequence. The present paper includes an investigation of the reachable workspace, a more general analysis of the control system underlying the model, its reachability and local controllability properties. In addition, we establish some fractal properties of the reachable workspace by means the theory of iterated function systems.

Real-time Inverse Kinematics of (2n + 1) DOF hyper-redundant manipulator arm via a combined numerical and analytical approach

The task of solving Inverse Kinematics (IK) for redundant serial chain manipulators has been and still continues to be quite challenging in the field of robotics. Researchers from different fields have succeeded in solving the IK of different robot configurations for various applications. However, the challenge of computational efficiency still remains, in particular for complex robot configurations, to be used for real-time applications. This paper presents a novel, computationally efficient method of performing IK for general 2n+1 (n is the number of joints) DOF manipulators with a spherical joint at the wrist. It uses the simplicity of analytical solutions to enhance the speed of numerical solvers that operate on each joint location individually. The problem of IK is approached as a constrained optimization, where obstacle avoidance and limit avoidance at joints are used as illustrations. The joint limitations are handled implicitly as boundary conditions for the numerical algorithm. The algorithm was executed and implemented on various paths for a 9 DOF arm and also simulated for a 13 DOF arm for generalization purposes.

Generating optimal reference kinematic configurations for hyper-redundant parallel robots

In this article, we propose an optimization process able to generate optimal kinematic configuration for spatial hyper-redundant manipulators with multiple rigid parallel modules. The proposed method uses a deterministic optimization scheme that evaluates the score of trial kinematic configurations while accounting for various geometric constraints. This versatile method is based on a simultaneous search for both the best curve capturing the overall kinematic robot posture and the platform distribution along this curve. This process is carried out using the powerful sequential quadratic programming technique. Numerical results are presented to illustrate the efficiency of the proposed approach. Finally, this model was validated by real measurements obtained with the continuum bionic handling arm of a mobile robot called Robotino-XT.

A new motion planning method for discretely actuated hyper-redundant manipulators

SUMMARYA hyper-redundant manipulator is made by mounting the serial and/or parallel mechanisms on top of each other as modules. In discrete actuation, the actuation amounts are a limited number of certain values. It is not feasible to solve the kinematic analysis problems of discretely actuated hyper-redundant manipulators (DAHMs) by using the common methods, which are used for continuous actuated manipulators. In this paper, a new method is proposed to solve the trajectory tracking problem in a static prescribed obstacle field. To date, this problem has not been considered in the literature. Theremoving first collision(RFC) method, which is originally proposed for solving the inverse kinematic problems in the obstacle fields was modified and used to solve the motion planning problem. For verification, the numerical results of the proposed method were compared with the results of thegenetic algorithm(GA) method. Furthermore, a novel DAHM designed and implemented by the authors is introduced.