scholarly journals Compliant behaviour of redundant robot arm - experiments with null-space

2015 ◽  
Vol 12 (1) ◽  
pp. 81-98
Author(s):  
Petar Petrovic ◽  
Nikola Lukic ◽  
Ivan Danilov
Keyword(s):  
Stiffness Matrix ◽  
Jacobian Matrix ◽  
Null Space ◽  
Joint Space ◽  
Robot Arm ◽  
Kinematic Redundancy ◽  
Redundant Robot ◽  
Redundant Robots ◽  
Compliant Behavior ◽  
Congruent Transformation

This paper presents theoretical and experimental aspects of Jacobian nullspace use in kinematically redundant robots for achieving kinetostatically consistent control of their compliant behavior. When the stiffness of the robot endpoint is dominantly influenced by the compliance of the robot joints, generalized stiffness matrix can be mapped into joint space using appropriate congruent transformation. Actuation stiffness matrix achieved by this transformation is generally nondiagonal. Off-diagonal elements of the actuation matrix can be generated by redundant actuation only (polyarticular actuators), but such kind of actuation is very difficult to realize practically in technical systems. The approach of solving this problem which is proposed in this paper is based on the use of kinematic redundancy and nullspace of the Jacobian matrix. Evaluation of the developed analytical model was done numerically by a minimal redundant robot with one redundant d.o.f. and experimentally by a 7 d.o.f. Yaskawa SIA 10F robot arm.

Design and Analysis of a Fully Actuated Cable-Driven Joint for Hyper-Redundant Robots with Optimal Cable Routing

2021 ◽  
pp. 1-13
Author(s):  
Paolo Guardiani ◽  
Daniele Ludovico ◽  
Alessandro Pistone ◽  
Haider Abidi ◽  
Isiah Zaplana ◽  
...  
Keyword(s):  
Genetic Algorithm ◽  
Optimization Method ◽  
Robot Arm ◽  
Redundant Robot ◽  
Redundant Robots ◽  
Routing Optimization ◽  
Novel Design

Abstract Cable-driven hyper-redundant robots have been adopted in many fields for accessing harsh and confined environments that maybe inaccessible or dangerous for humans. The cable actuation strategy makes the robot hardware safer and increases the robot payload reducing its weight. In this paper, a novel design of a fully actuated cable-driven hyper-redundant robot has been proposed. This solution is a pulleyless design that decreases the mechanical complexity, allowing to reduce the robot arm diameter and avoid tension losses on the cables during the motion. Three different joint designs have been taken into account and experiments have been carried to study their performances. The kinematics for n-joint robot has been formulated and a cable routing optimization method based on genetic algorithm have been proposed and applied to a five-joints robot.

Experiments with Force Control of Redundant Robots in Unstructured Environment Using Minimal Null-space Formulation

2001 ◽  
Vol 5 (5) ◽  
pp. 263-268
Author(s):  
Bojan Nemec ◽  
◽  
Leon Zlajpah Institute Jozef Stefan
Keyword(s):  
Force Control ◽  
Null Space ◽  
Robot Arm ◽  
End Effector ◽  
Redundant Robots ◽  
Unstructured Environment ◽  
Space Formulation ◽  
Null Space Approach ◽  
Selection Of ◽  
Space Approach

The paper describes the implementation of the force control for redundant robots in an unstructured environment. We assume that the obstacles are not known in advance. Hence, the robot arm has to be compliant with the environment while tracking the desired position and force at the end effector. Using the minimal null space approach the appropriate impedance controller, which decouples the end effector and the null space spaces was derived. The control algorithm enables the selection of dynamic characteristics in both subspaces independently.The proposed method was verified with the simulation and with experiments on a 4 D.O.F planar redundant robot.

Comparison of null-space and minimal null-space control algorithms

Robotica ◽  
2007 ◽  
Vol 25 (5) ◽  
pp. 511-520 ◽  
Author(s):  
Bojan Nemec ◽  
Leon Žlajpah ◽  
Damir Omrčen
Keyword(s):  
Degrees Of Freedom ◽  
Null Space ◽  
Space Velocity ◽  
Control Algorithms ◽  
Robot Arm ◽  
Velocity Control ◽  
Redundant Robots ◽  
Operational Space ◽  
Space Projection ◽  
The Stability

SUMMARYThis paper deals with the stability of null-space velocity control algorithms in extended operational space for redundant robots. We compare the performance of the control algorithm based on the minimal null-space projection and generalized-inverse-based projection into the Jacobian null-space. We show how the null-space projection affects the performance of the null-space tracking algorithm. The results are verified with the simulation and real implementation on a redundant mobile robot composed of 3 degrees of freedom (DOFs) mobile platform and 7-DOF robot arm.

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

2019 ◽  
Vol 39 (4) ◽  
pp. 696-714
Author(s):  
Nikola Lukic ◽  
Petar B. Petrovic
Keyword(s):  
Control System ◽  
Null Space ◽  
Open Architecture ◽  
Robot Arm ◽  
Task Space ◽  
Simulation Experiments ◽  
Redundant Robot ◽  
Content Type ◽  
Physical Experiments ◽  
Stiffness Control

Purpose Stiffness 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/approach Theoretical 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. Findings Simulation 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/value A 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.

scholarly journals Iterative Learning without Reinforcement or Reward for Multijoint Movements: A Revisit of Bernstein's DOF Problem on Dexterity

2010 ◽  
Vol 2010 ◽  
pp. 1-15
Author(s):  
Suguru Arimoto ◽  
Masahiro Sekimoto ◽  
Kenji Tahara
Keyword(s):  
Inverse Kinematics ◽  
Degrees Of Freedom ◽  
Joint Space ◽  
Iterative Learning ◽  
Joint Control ◽  
Robot Arm ◽  
Kinematic Redundancy ◽  
History Of ◽  
The Central Nervous System ◽  
Multijoint Movements

A robot designed to mimic a human becomes kinematically redundant and its total degrees of freedom becomes larger than the number of physical variables required for describing a given task. Kinematic redundancy may contribute to enhancement of dexterity and versatility but it incurs a problem of ill-posedness of inverse kinematics from the task space to the joint space. This ill-posedness was originally found by Bernstein, who tried to unveil the secret of the central nervous system and how nicely it coordinates a skeletomotor system with many DOFs interacting in complex ways. In the history of robotics research, such ill-posedness has not yet been resolved directly but circumvented by introducing an artificial performance index and determining uniquely an inverse kinematics solution by minimization. This paper tackles such Bernstein's problem and proposes a new method for resolving the ill-posedness in a natural way without invoking any artificial index. First, given a curve on a horizontal plane for a redundant robot arm whose endpoint is imposed to trace the curve, the existence of a unique ideal joint trajectory is proved. Second, such a uniquely determined motion can be acquired eventually as a joint control signal through iterative learning without reinforcement or reward.

scholarly journals Design and Validation of a Novel Cable-Driven Hyper-Redundant Robot Based on Decoupled Joints

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Long Huang ◽  
Bei Liu ◽  
Lairong Yin ◽  
Peng Zeng ◽  
Yuanhan Yang
Keyword(s):  
Control System ◽  
Coupling Effect ◽  
Kinematic Model ◽  
Joint Space ◽  
Degree Of Freedom ◽  
Driving Mechanism ◽  
Coupling Effects ◽  
Redundant Robot ◽  
Redundant Robots ◽  
Universal Joints

In most of the prior designs of conventional cable-driven hyper-redundant robots, the multiple degree-of-freedom (DOF) bending motion usually has bending coupling effects. It means that the rotation output of each DOF is controlled by multiple pairs of cable inputs. The bending coupling effect will increase the complexity of the driving mechanism and the risk of slack in the driving cables. To address these problems, a novel 2-DOF decoupled joint is proposed by adjusting the axes distribution of the universal joints. Based on the decoupled joint, a 4-DOF hyper-redundant robot with two segments is developed. The kinematic model of the robot is established, and the workspace is analyzed. To simplify the driving mechanism, a kinematic fitting approach is presented for both proximal and distal segments and the mapping between the actuator space and the joint space is significantly simplified. It also leads to the simplification of the driving mechanism and the control system. Furthermore, the cable-driven hyper-redundant robot prototype with multiple decoupled joints is established. The experiments on the robot prototype verify the advantages of the design.

Manipulator system designs for drawing random objects through point cloud posture estimation

2021 ◽  
pp. 095440542097946
Author(s):  
Ching-Chang Wong ◽  
Hsuan Ming Feng ◽  
Yu-Cheng Lai ◽  
Hsiang-Yun Chen
Keyword(s):  
Point Cloud ◽  
Null Space ◽  
Robot Manipulator ◽  
Search Algorithm ◽  
Movement Control ◽  
Control Policy ◽  
Device Management ◽  
Redundant Robot ◽  
Better Regulation ◽  
The Right

This paper designed a 7-DOF redundant robot manipulator that can flexibly and efficiently pick-up random objects. The developed 7-DOF machine with an additional redundancy achieved great progress in terms of flexibility and efficiency in the operational space. A robot operating system (ROS) was used to configure the manipulator system’s software modules, supporting convenient system interface, appropriate movement control policy, and powerful hardware device management for better regulation of the manipulator’s motions. A 3D type Point Cloud Library (PCL) was utilized to perform a novel point cloud image pre-processing method that did not only reduce the point cloud number but also maintained the original quality. The results of the experiment showed that the estimation speed in object detection and recognition procedure improved significantly. The redundant robot manipulator architecture with the two-stage search algorithm was able to find the optimal null space. Suitable parameters in D-H transformation of forward kinematics were selected to efficiently control and position the manipulator in the right posture. Meanwhile, the reverse kinematics estimated all angles of the joints through the known manipulator position, orientation, and redundancy. Finally, motion panning implementation of manipulator rapidly and successfully reached the random object position and automatically drew it up to approximate the desired target.

ROBOTIC HANDWRITING

2005 ◽  
Vol 02 (01) ◽  
pp. 105-124 ◽  
Author(s):  
VELJKO POTKONJAK
Keyword(s):  
Mathematical Models ◽  
Muscle Fatigue ◽  
Simulation Study ◽  
Robot Control ◽  
Robot Arm ◽  
Redundancy Resolution ◽  
Kinematic Redundancy ◽  
New Concepts ◽  
Human Arm ◽  
Arm Motion

Handwriting has always been considered an important human task, and accordingly it has attracted the attention of researchers working in biomechanics, physiology, and related fields. There exist a number of studies on this area. This paper considers the human–machine analogy and relates robots with handwriting. The work is two-fold: it improves the knowledge in biomechanics of handwriting, and introduces some new concepts in robot control. The idea is to find the biomechanical principles humans apply when resolving kinematic redundancy, express the principles by means of appropriate mathematical models, and then implement them in robots. This is a step forward in the generation of human-like motion of robots. Two approaches to redundancy resolution are described: (i) "Distributed Positioning" (DP) which is based on a model to represent arm motion in the absence of fatigue, and (ii) the "Robot Fatigue" approach, where robot movements similar to the movements of a human arm under muscle fatigue are generated. Both approaches are applied to a redundant anthropomorphic robot arm performing handwriting. The simulation study includes the issues of legibility and inclination of handwriting. The results demonstrate the suitability and effectiveness of both approaches.

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