Redundant Arm Research Articles

Semantic composition of robotic solver algorithms on graph structures

This article introduces a model-based design, implementation, deployment, and execution methodology, with tools supporting the systematic composition of algorithms from generic and domain-specific computational building blocks that prevent code duplication and enable robots to adapt their software themselves. The envisaged algorithms are numerical solvers based on graph structures. In this article, we focus on kinematics and dynamics algorithms, but examples such as message passing on probabilistic networks and factor graphs or cascade control diagrams fall under the same pattern. The tools rely on mature standards from the Semantic Web. They first synthesize algorithms symbolically, from which they then generate efficient code. The use case is an overactuated mobile robot with two redundant arms.

On-orbit transportation with non-conserved momenta by cooperative space robots

The demands of on-orbit transporting large structures via multiple space robots are emerging in space applications to increase the limited transportation capability of single space robots. However, the high level of system coupling arising from the increased number of individuals and physical interaction between structures and robots brings great challenges to the consequent control. This paper focuses on the motion planning of collaboratively transporting a large space structure using rigidly connected space robots. First, the system model is established at a kinematic level with non-conserved momenta due to the effects of thrusters on the bases of robots. Then, a cooperative control model is formulated to minimize the fuel consumption by balancing the thrusts and torques respectively acting on the bases and redundant arm joints of space robots. The physical limitations of space robots and mission related constraints such as joint angle limits, control input saturation and collision avoidance for multiple space obstacles are also taken into account in the optimization. Afterwards, the effectiveness of the proposed control scheme is validated and demonstrated by numerical case studies.

Coordinating Obstacle Avoidance of a Redundant Dual-Arm Nursing-Care Robot.

Collision safety is an essential issue for dual-arm nursing-care robots. However, for coordinating operations, there is no suitable method to synchronously avoid collisions between two arms (self-collision) and collisions between an arm and the environment (environment-collision). Therefore, based on the self-motion characteristics of the dual-arm robot's redundant arms, an improved motion controlling algorithm is proposed. This study introduces several key improvements to existing methods. Firstly, the volume of the robotic arms was modeled using a capsule-enveloping method to more accurately reflect their actual structure. Secondly, the gradient projection method was applied in the kinematic analysis to calculate the shortest distances between the left arm, right arm, and the environment, ensuring effective avoidance of the self-collision and environment-collision. Additionally, distance thresholds were introduced to evaluate collision risks, and a velocity weight was used to control the smooth coordinating arm motion. After that, experiments of coordinating obstacle avoidance showed that when the redundant dual-arm robot is holding an object, the coordinating operation was completed while avoiding self-collision and environment-collision. The collision-avoidance method could provide potential benefits for various scenarios, such as medical robots and rehabilitating robots.

Human arm redundancy: a new approach for the inverse kinematics problem.

The inverse kinematics (IK) problem addresses how both humans and robotic systems coordinate movement to resolve redundancy, as in the case of arm reaching where more degrees of freedom are available at the joint versus hand level. This work focuses on which coordinate frames best represent human movements, enabling the motor system to solve the IK problem in the presence of kinematic redundancies. We used a multi-dimensional sparse source separation method to derive sets of basis (or source) functions for both the task and joint spaces, with joint space represented by either absolute or anatomical joint angles. We assessed the similarities between joint and task sources in each of these joint representations, finding that the time-dependent profiles of the absolute reference frame's sources show greater similarity to corresponding sources in the task space. This result was found to be statistically significant. Our analysis suggests that the nervous system represents multi-joint arm movements using a limited number of basis functions, allowing for simple transformations between task and joint spaces. Additionally, joint space seems to be represented in an absolute reference frame to simplify the IK transformations, given redundancies. Further studies will assess this finding's generalizability and implications for neural control of movement.

Torque control of a wheeled humanoid robot with dual redundant arms

Most of conventional controllers are prone to consume more computational time for controlling a wheeled humanoid robot. A nonlinear trajectory control of a wheeled humanoid robot using a model-based controller with less computational load and energy consumption is presented in this article. The upper body of the humanoid robot consists of two 6 degrees of freedom redundant arms, a three degrees of freedom torso and a two degrees of freedom neck. The nonholonomic mobile platform consists of two actuated wheels and two caster wheels. Nonlinearity of the robot dynamic model and coupling between various branches of the upper body are taken into account. The dynamic model derived using Newton–Euler approach along with decoupled Natural Orthogonal Complement matrix approach is used to derive dynamic equations of the upper body and the wheeled platform. Zero moment point based stability approach is used for verifying stable motion of the wheeled humanoid robot with minimum energy and time consumption to complete a task. The proposed computed torque controller is compared with other similar controllers developed for the same robot model to prove advantages of the proposed torque controller. Simulation results are experimentally validated with the real robot.

Reinforcement Learning with Dynamic Movement Primitives for Obstacle Avoidance

Dynamic movement primitives (DMPs) are a robust framework for movement generation from demonstrations. This framework can be extended by adding a perturbing term to achieve obstacle avoidance without sacrificing stability. The additional term is usually constructed based on potential functions. Although different potentials are adopted to improve the performance of obstacle avoidance, the profiles of potentials are rarely incorporated into reinforcement learning (RL) framework. In this contribution, we present a RL based method to learn not only the profiles of potentials but also the shape parameters of a motion. The algorithm employed is PI2 (Policy Improvement with Path Integrals), a model-free, sampling-based learning method. By using the PI2, the profiles of potentials and the parameters of the DMPs are learned simultaneously; therefore, we can optimize obstacle avoidance while completing specified tasks. We validate the presented method in simulations and with a redundant robot arm in experiments.

Pose control of constrained redundant arm using recurrent neural networks and one-iteration computing algorithm

Accuracy and safety are two important factors in redundant arm control. Generally, physical constraints should be taken into account for safe operation of redundant arm. By investigating the kinematics of redundant arm, the formulation of end-effector’s position and orientation is presented in detail. By utilizing zeroing neural network method, a pose control scheme considering physical constraints is proposed. For solving the pose control scheme, it is reformulated as a standard quadratic programming at joint angular velocity level. Then, a projection neural network solver is developed to handle the quadratic programming. Further, for better computer operation and real-time requirements, the discrete algorithm is desired. As a result, a one-iteration computing algorithm is developed for pose control of redundant arm by discretizing the projection neural network solver. Theoretical results are presented to guarantee the properties of the proposed scheme and the one-iteration computing algorithm. In addition, plenty of comparative experiments on the basis of UR5 arm verify the efficacy and superiority of the one-iteration computing algorithm, and substantiate theoretical results.

A New Approach to Fault Detection in the Power Converter in Wind Turbine Conversion Systems

The detection of faults in a wind turbine chain is of prime importance in order to maintain safety, enhance reliability and improve economic performance. In addition, wind systems have to ensure a continuity of service for a considerable period of time in the event of an electrical fault in the network or a fault in one of the elements of the electromechanical conversion system. This paper presents a fault detection methodology of the power converter within a wind turbine chain, equipped with a Doubly-Fed Induction Generator (DFIG). A configurable, fast, and accurate scheme is developed, the basis of which is the reliable identification of the failed switch. The solution proposed in this work involves the deployment of a redundant arm in the event of a fault; the replacement arm is utilized while waiting for a maintenance or repair operation to be carried out. The approach developed in this paper provides continuity of service after the occurrence of a fault in the network system and fault detection time is reduced. The validity of the proposed identification methodology is assessed by means of simulation of the model of a wind turbine conversion system.

Dexterity analysis and intelligent trajectory planning of redundant dual arms for an upper body humanoid robot

PurposeMost of the redundant dual-arm robots are singular free, dexterous and collision free compared to other robotic arms. This paper aims to analyse the workspace of redundant arms to study the manipulability. Furthermore, multi-layer perceptron (MLP) algorithm is used to determine the various joint parameters of both the upper body redundant arms. Trajectory planning of robotic arms is carried out with the help of inverse solutions obtained from the MLP algorithm.Design/methodology/approachIn this paper, the kinematic equations are derived from screw theory approach and inverse kinematic solutions are determined using MLP algorithm. Levenberg–Marquardt (LM) and Bayesian regulation (BR) techniques are used as the backpropagation algorithms. The results from two backpropagation techniques are compared for determining the prediction accuracy. The inverse solutions obtained from the MLP algorithm are then used to optimize the cubic spline trajectories planned for avoiding collision between arms with the help of convex optimization technique. The dexterity of the redundant arms is analysed with the help of Cartesian workspace of arms.FindingsDexterity of redundant arms is analysed by studying the voids and singular spaces present inside the workspace of arms. MLP algorithms determine unique solutions with less computational effort using BR backpropagation. The inverse solutions obtained from MLP algorithm effectively optimize the cubic spline trajectory for the redundant dual arms using convex optimization technique.Originality/valueMost of the MLP algorithms used for determining the inverse solutions are used with LM backpropagation technique. In this paper, BR technique is used as the backpropagation technique. BR technique converges fast with less computational time than LM method. The inverse solutions of arm joints for traversing optimized cubic spline trajectory using convex optimization technique are computed from the MLP algorithm.

Self‐feeding assistive 7‐DOF robotic arm simulator using solving method of inverse kinematics

AbstractIn order to help people with disabilities of the upper extremities drink and eat, a simulator for self‐feeding assistive robotic arm using solving method of inverse kinematics has been developed in this paper. Using inverse kinematics equations of 7 degrees of freedom (DOF) with an arm angle parameter, the robotic arm model was implemented in the simulator and its controller with mouse device was also designed. The arm angle parameter defined the angle between the arm plane and a reference plane was used to resolve the robotic arm redundancy. Three able‐bodied persons participated in simulation experiments. They manipulated the robotic arm model in a virtual space using mouse device. It was found from the simulation results they successfully performed the drinking and eating tasks in our simulator.

Motion specification algorithms for both platform and arms of a mobile robot for planetary research

This article describes some aspects of the control system design for a four-wheel mobile platform with individual wheel-steering equipped with two redundant robotic arms. The considered control issues include different ways of platform maneuvering as well as a solution of inverse kinematics problem for a redundant arm with an original approach to redundancy resolution depending on operator’s intention.

Design and control of a 7 DOF redundant manipulator arm

ABSTRACT With the development of science and technology, robots have become an integral part of human life. To ease human efforts in tedious and repetitive tasks, robots are used in human platforms. The current analysis is focused on the design and development of a robotic manipulator to perform pick and place like operations. First, the kinematic analysis is performed on different links of the designed manipulator to know its workspace and singularity. Each link of the manipulator is modelled in SOLIDWORKS software and simultaneously imported to V-REP software. In the V-REP software, links are grouped to form the manipulator arm. Each link is attached to a joint. After formation of the manipulator arm, simulations for different physical operations are performed. While performing different physical operations with the manipulator arm, graphical analysis is performed for position, velocity and acceleration of revolute joints. The force required for the prismatic joint to hold the object is also calculated. The results obtained from the simulation analysis reveal that the manipulator can work satisfactorily in the practical environment. Finally, the results are compared for manipulators of different degrees of freedom to obtain the workspace required for a smooth operation. The current study holds a large importance in robotics field as mobile manipulators are extensively used in different industries and the same analysis can also be extended towards other forms robots. Abbreviation: DLS: Damped Least Square DH: Denavit-Hartenberg V-REP: Virtual Robot Experimentation Platform IK: Inverse Kinematics

Complementary projector for null-space stiffness control of redundant assembly robot arm

PurposeStiffness control of redundant robot arm, aimed at using extra degrees of freedom (DoF) to shape the robot tool center point (TCP) elastomechanical behavior to be consistent with the essential requirements needed for a successful part mating process, i.e., to mimic part supporting mechanism with selective quasi-isotropic compliance (Remote Center of Compliance – RCC), with additional properties of inherent flexibility.Design/methodology/approachTheoretical analysis and synthesis of the complementary projector for null-space stiffness control of kinematically redundant robot arm. Practical feasibility of the proposed approach was proven by extensive computer simulations and physical experiments, based on commercially available 7 DoF SIA 10 F Yaskawa articulated robot arm, equipped with the open-architecture control system, system for generating excitation force, dedicated sensory system for displacement measurement and a system for real-time acquisition of sensory data.FindingsSimulation experiments demonstrated convergence and stability of the proposed complementary projector. Physical experiments demonstrated that the proposed complementary projector can be implemented on the commercially available anthropomorphic redundant arm upgraded with open-architecture control system and that this projector has the capacity to efficiently affect the task-space TCP stiffness of the robot arm, with a satisfactory degree of consistency with the behavior obtained in the simulation experiments.Originality/valueA novel complementary projector was synthesized based on the adopted objective function. Practical verification was conducted using computer simulations and physical experiments. For the needs of physical experiments, an adequate open-architecture control system was developed and upgraded through the implementation of the proposed complementary projector and an adequate system for generating excitation and measuring displacement of the robot TCP. Experiments demonstrated that the proposed complementary projector for null-space stiffness control is capable of producing the task-space TCP stiffness, which can satisfy the essential requirements needed for a successful part-mating process, thus allowing the redundant robot arm to mimic the RCC supporting mechanism behavior in a programmable manner.

Kinematic Redundancy Analysis during Goal-Directed Motion for Trajectory Planning of an Upper-Limb Exoskeleton Robot.

The kinematic redundancy of human arm imposes challenges on joint space trajectory planning for upper-limb rehabilitation robot. This paper aims to investigate normal motion patterns in reaching and reach-to-grasp movements, and obtain the unique solution in joint space for a five-DOF exoskeleton. Firstly, a six-camera optical motion tracking system was used to capture participants' arm motion during goal-directed reaching or reach-to-grasp movements. Secondly, statistical analysis was executed to explore the characteristics of swivel angle, which revealed that the swivel angle can be approximated to the mean value (155° ± 5°) in resolving the arm redundancy problem. Thirdly, combined with the minimum-jerk trajectory of end-effector, the generated joint trajectory complied well with the joint trajectory captured in healthy humans. Consequently, the obtained results facilitate a new way for three-dimensional trajectory planning of the exoskeleton robot. Further, adaptive assist-as-needed control of the exoskeleton robot can be implemented based on the optimal reference trajectory, with aims to provide assistance according to the patient's performance, and in turn promote neural plasticity.

Flying watch: an attachable strength enhancement device for long-reach robotic arms

A long-reach robotic arm is useful for applications such as nuclear plant decommissioning, inspection, and firefighting. However, for such arms, a small external reaction force can result in large loads on proximal arm actuators because of long moment arms. This problem was previously solved by specialized arm designs that compensate external reaction forces. However, these arm designs are hard to be applied to other arms or customized to different missions. To overcome these difficulties, in this paper, we propose a modular thrust generating concept inspired by wristwatch designs, called flying watch, which can be attached to a robotic arm with mission-dependent attachment styles (attachment positions and orientations) and cooperate with actuators to enhance arm strength. We first introduce flying watch concept, design, and dynamics. Then we propose two levels of watch-actuator cooperation in quasistatic situations by introducing a problem called Watch Actuator Cooperation for Arm Enhancement (WACAE) and providing an example solution. The first level of cooperation is only watches adapt their thrusts to minimize actuator loads, which is generally applicable to varieties of arms. The second level cooperation is that not only do the watches adapt their thrusts but also the actuators cooperatively position the watches to optimal positions and orientations to counteract external reaction forces, which is suitable for redundant arms and can counteract external reaction forces more effectively. Finally, we present simulations to verify that flying watches can significantly reduce actuator loads using both levels of watch-actuator cooperation (the first level by 36.9% and the second level by 43.7%).

Neural Network Control of Space Manipulator Based on Dynamic Model and Disturbance Observer

Space flexible manipulators are convenient for performing on-orbit service; however, the vibration of the end effector is becoming increasingly serious because of the excessive length and mass of the arm. To solve this problem, in this paper, neural network control based on a flexible multibody dynamic model and disturbance observer is proposed. The dynamics model is based on the Lagrangian equation and assumed mode method, and also considers the position and attitude constraint equations of the flexible joint. The combination of a neural network controller and adaptive controller is introduced in detail, and a switching mechanism is added to improve the global stability of the system. Considering the joint module as an independent control system, a disturbance observer is added to the current loop of the control system, and a filter is combined to effectively suppress the influence of friction and dynamic coupling on joint control performance. The effectiveness of the proposed dynamic model and control scheme in terms of vibration suppression is verified in experiments on the self-designed space flexible redundant arm.

An efficient motion generation method for redundant humanoid robot arms based on motion continuity

ABSTRACTThis paper proposes a novel method of motion generation for redundant humanoid robot arms, which can efficiently generate continuous collision-free arm motion for the preplanned hand trajectory. The proposed method generates the whole arm motion first and then computes the actuators’ motion, which is different from IK (inverse kinematics)-based motion generation methods. Based on the geometric constraints of the preplanned trajectory and the geometric structure of humanoid robot arms, the wrist trajectory and elbow trajectory can be got first without solving inverse kinematics and forward kinematics. Meanwhile, the constraints restrict all feasible arm configurations to an elbow-circle and reduce the arm configuration space to a two-dimension space. By combining the configuration space and collision distribution of arm motion, collision-free arm configurations can be identified and be used to generate collision-free arm motion, which can avoid unnecessary forward and inverse kinematics. The experiments show that the proposed method can generate continuous and collision-free arm motion for preplanned hand trajectories.

The Effects of Selective Muscle Weakness on Muscle Coordination in the Human Arm.

Despite the fundamental importance of muscle coordination in daily life, it is currently unclear how muscle coordination adapts when the musculoskeletal system is perturbed. In this study, we quantified the impact of selective muscle weakness on several metrics of muscle coordination. Seven healthy subjects performed 2D and 3D isometric force target matches, while electromyographic (EMG) signals were recorded from 13 elbow and shoulder muscles. Subsequently, muscle weakness was induced by a motor point block of brachialis muscle. Postblock subjects repeated the force generation tasks. We quantified muscle coordination pre- and postblock using three metrics: tuning curve preferred direction, tuning curve area, and motor modules analysis via nonnegative matrix factorization. For most muscles, the tuning direction for the 2D protocol was not substantially altered postblock, while tuning areas changed more drastically. Typically, five motor modules were identified from the 3D task, and four motor modules were identified in the 2D task; this result held across both pre- and postblock conditions. The composition of one or two motor modules, ones that involved mainly the activation of shoulder muscles, was altered postblock. Our results demonstrate that selective muscle weakness can induce nonintuitive alternations in muscle coordination in the mechanically redundant human arm.

Reliability model of bond wire fatigue for IGBT in MMC with system redundancy consideration

Reliability is a significant factor in the operation of the modular multilevel converter (MMC). Since the bond wire fatigue is one of the dominant failures of the insulated-gate bipolar transistor (IGBT) in the aging aspect, the wire bond lifetime related research has captured much attention in recent years. However, at system level, the redundancy of the system is seldom discussed in the reliability analysis of MMC. This paper proposes a reliability model for wire bond failure of IGBT with system redundancy consideration. The reliability model for IGBT at the component level is established based on the lifetime model. Also, the reliability model for the system with redundancy is built by the end-of-life cumulative distribution obtained from Monte Carlo method. The unreliability change of system level and component level are compared, and the influence of bridge arm redundancy on system reliability is also analyzed.

An Uncontrolled Manifold Analysis of Arm Joint Variability in Virtual Planar Position and Orientation Telemanipulation.

In teleoperated robot-assisted tasks, the user interacts with manipulators to finely control remote tools. Manipulation of robotic devices, characterized by specific kinematic and dynamic proprieties, is a complex task for the human sensorimotor system due to the inherent biomechanical and neuronal redundancies that characterize the human arm and its control. We investigate how master devices with different kinematics structures and how different task constraints influence users capabilities in exploiting arm redundancy. A virtual teleoperation workbench was designed and the arm kinematics of seven users was acquired during the execution of two planar virtual tasks, involving either the control of position only or position-orientation of a tool. Using the uncontrolled manifold analysis of arm joint variability, we estimated the logarithmic ratio between the task irrelevant and the task relevant manifolds ( Rv). The Rv values obtained in the position-orientation task were higher than in the position only task, while no differences were found between the master devices. A modulation of Rv was found through the execution of the position task and a positive correlation was found between task performance and redundancy exploitation. Users exploited additional portions of arm redundancy when dealing with the tool orientation. The Rv modulation seems influenced by the task constraints and by the users possibility of reconfiguring the arm position. This paper advances the general understanding of the exploitation of arm redundancy in complex tasks, and can improve the development of future robotic devices.