scholarly journals A Comparison of Policy Search in Joint Space and Cartesian Space for Refinement of Skills

2019 ◽  
pp. 301-309 ◽  
Author(s):  
Alexander Fabisch
Keyword(s):  
Joint Space ◽  
Policy Search ◽  
Cartesian Space

scholarly journals Regions of Feasible Point-to-Point Trajectories in the Cartesian Workspace of Fully-Parallel Manipulators

1999 ◽  
Author(s):  
Damien Chablat ◽  
Philippe Wenger
Keyword(s):  
Parallel Manipulator ◽  
Cartesian Product ◽  
Parallel Manipulators ◽  
Joint Space ◽  
Inverse Kinematic ◽  
Connected Components ◽  
Feasible Point ◽  
Cartesian Space ◽  
Point Trajectories ◽  
Point To Point

Abstract The goal of this paper is to define the n-connected regions in the Cartesian workspace of fully-parallel manipulators, i.e. the maximal regions where it is possible to execute point-to-point motions. The manipulators considered in this study may have multiple direct and inverse kinematic solutions. The N-connected regions are characterized by projection, onto the Cartesian workspace, of the connected components of the reachable configuration space defined in the Cartesian product of the Cartesian space by the joint space. Generalized octree models are used for the construction of all spaces. This study is illustrated with a simple planar fully-parallel manipulator.

The Control of Hexapod Parallel Mechanism

2012 ◽  
Vol 195-196 ◽  
pp. 1030-1034
Author(s):  
Chun Ping Pan ◽  
Hsin Guan
Keyword(s):  
Tracking Error ◽  
Joint Space ◽  
Variable Load ◽  
Phase Lag ◽  
Parallel Mechanisms ◽  
Nonlinear Controller ◽  
Cartesian Space ◽  
Motion System ◽  
Wide Range ◽  
System Output

In order to enhance the innervations fidelity of simulators, an adaptive nonlinear controller is developed, which guarantees parallel mechanisms closed loop system global asymptotical stability and the convergence of posture tracking error in Cartesian space. The problem of rapid tracking under the condition of the wide range, nonlinear and variable load is solved. After the adaptive nonlinear controller is actually applied to the hexapod parallel mechanisms of simulator, the dynamic-static capabilities of motion system is tested by amplitude-frequency response and posture precision. The experimental results show that the static precision improves ten times and system output amplitude increase and the phase lag reduce with respect to the same input signal in Cartesian space in comparison with the traditional proportional and derivative controlling method in joint space. Therefore the adaptive nonlinear controller can effectively improve the dynamic-static response performance of the hexapod parallel mechanisms of simulators in Cartesian space.

scholarly journals Kinematic analysis of a newly designed cable-driven manipulator

2018 ◽  
Vol 42 (2) ◽  
pp. 125-135 ◽  
Author(s):  
Wei Xu ◽  
Yaoyao Wang ◽  
Surong Jiang ◽  
Jiafeng Yao ◽  
Bai Chen
Keyword(s):  
Trajectory Planning ◽  
Kinematic Analysis ◽  
Joint Space ◽  
Joint Angles ◽  
Coupled Motion ◽  
Cartesian Space ◽  
The Impact ◽  
The Relationship

In this paper, the cable routing configurations for a cable-driven manipulator are introduced, and the impact of motion coupling caused by cable transmission routing of a 2n type cable-driven manipulator is analyzed in detail. Based on different configurations of cable routings, the relationship between variation of joint angles and the geometrical sizes of guide pulleys is established, represented by a matrix for coupled motion. Moreover, based on the effects of the motion coupling of a cable-driven manipulator, we propose the condition for the invariance of orientation, which can be achieved constraining of the geometrical sizes of guide pulleys and driven wheels. In addition, to identify the correctness of analysis for coupled motion, a 3-DOFs planer cable-driven manipulator prototyping model is constructed, and the kinematics and trajectory planning has been solved. Finally, the relationship among actuator space, joint space, and Cartesian space, including the mapping of the motion coupling, is experimentally validated. The property of invariance of orientation is also validated by an experiment.

A 3-ṞPR Parallel Mechanism With Singularities That are Self-Motions

2010 ◽  
Vol 2 (3) ◽  
Author(s):  
Novona Rakotomanga ◽  
Ilian A. Bonev
Keyword(s):  
Parallel Mechanism ◽  
Control Strategies ◽  
Joint Space ◽  
Degree Of Freedom ◽  
Parallel Mechanisms ◽  
Active Joint ◽  
Cartesian Space ◽  
Three Degree Of Freedom

The Cartesian workspace of most three-degree-of-freedom parallel mechanisms is divided by Type 2 (also called parallel) singularity surfaces into several regions. Accessing more than one such region requires crossing a Type 2 singularity, which is risky and calls for sophisticated control strategies. Some mechanisms can still cross these Type 2 singularity surfaces through “holes” that represent Type 1 (also called serial) singularities only. However, what is even more desirable is if these Type 2 singularity surfaces were curves instead. Indeed, there exists at least one such parallel mechanism (the agile eye) and all of its singularities are self-motions. This paper presents another parallel mechanism, a planar one, whose singularities are self-motions. The singularities of this novel mechanism are studied in detail. While the Type 2 singularities in the Cartesian space still constitute a surface, they degenerate into lines in the active-joint space, which is the main result of this paper.

Feasible Motion Solutions for Serial Manipulators at Singular Configurations

2003 ◽  
Vol 125 (1) ◽  
pp. 61-69 ◽  
Author(s):  
Yuefa Fang ◽  
Lung-Wen Tsai
Keyword(s):  
Degrees Of Freedom ◽  
Jacobian Matrix ◽  
Full Rank ◽  
Joint Space ◽  
Serial Manipulators ◽  
First Order ◽  
Singular Configurations ◽  
Cartesian Space ◽  
Novel Approach ◽  
Singular Configuration

When a serial manipulator is at a singular configuration, the Jacobian matrix will lose its full rank causing the manipulator to lose one or more degrees of freedom. This paper presents a novel approach to model the manipulator kinematics and solve for feasible motions of a manipulator at singular configurations such that the precise path tracking of a manipulator at such configurations is possible. The joint screw linear dependency is determined by using known line varieties so that not only the singular configurations of a manipulator can be identified but also the dependent joint screws can be determined. Feasible motions in Cartesian space are identified by using the theory of reciprocal screws and the resulting equations of constraint. The manipulator first-order kinematics is then modeled by isolating the linearly dependent columns and rows of the Jacobian matrix such that the mapping between the feasible motions in Cartesian space and the joint space motions can be uniquely determined. Finally, a numerical example is used to demonstrate the feasibility of the approach. The simulation results show that a PUMA-type robot can successfully track a path that is singular at all times.

scholarly journals Path optimization for robots in a constrained workspace

2019 ◽  
Vol 8 (2) ◽  
pp. 89
Author(s):  
Doaa Mahmood Badr ◽  
Abbas Fadhal Mahdi
Keyword(s):  
Optimal Path ◽  
Joint Space ◽  
Task Space ◽  
Dimensional Synthesis ◽  
A Algorithm ◽  
Cartesian Space ◽  
Optimum Path ◽  
Stepper Motors ◽  
Path Planner

In this work, the classical A* algorithm serves as path planner to generate the optimum path that would avoid collisions and take the start, collisions, and goal as an input and give the optimal path as an output. The work was done in a static environment, so the coordinates of the obstacles are predefined for the planner. The obtained path is just a sequence of points in space, and this path may be considered later the task space and the first step for another sequential operation like mapping from Cartesian space to joint space, topology optimization, dimensional synthesis, etc. The case study was Lab-Volt 5150 manipulator; it is an accurate educational five degree of freedom 5DOF stationary robot driven by five stepper motors.

Application of SMC and NLFC Into a PRRR Robotic Arm

2014 ◽  
Author(s):  
Khaled S. Hatamleh ◽  
Mohammad Al-Shabi ◽  
Qais A. Khasawneh ◽  
Mohammad Abo Al-Asal
Keyword(s):  
Sliding Mode ◽  
Joint Space ◽  
Robotic Arm ◽  
Linear Feedback ◽  
Dynamics Modeling ◽  
Model Uncertainties ◽  
Space Trajectories ◽  
Modeling And Control ◽  
Robotic Arms ◽  
Cartesian Space

Industrial robotic arms are widely used nowadays. Accuracy and efficiency that fulfill user’s requirements are achieved through robust controller. This paper investigates dynamics modeling and control of a four DOF (PRRR) robot that is dedicated to perform a Pick-and-Place move of a certain product. The arm is undergoing manufacturing process. Forward and inverse kinematics solutions are introduced to solve the joint space trajectories associated with the desired End Effector (EE) Cartesian space path. The performance of two controllers under the presence of model uncertainties is inspected through a simulation study; Non-Linear Feedback Control (NLFC) and Sliding Mode Control (SMC) are designed and tested over the required joint space trajectories and Cartesian space path. Results showed that NLFC achieved better results than SMC in terms of RMSE when model uncertainties were absent. However, when model uncertainties were introduced, SMC performance was more robust than NLFC. Simulation results are very encouraging towards using the SMC over the actual robotic arm.

Look-ahead-window-based interval adaptive feedrate scheduling for long five-axis spline toolpaths under axial drive constraints

2020 ◽  
Vol 234 (13) ◽  
pp. 1656-1670
Author(s):  
De-Ning Song ◽  
Yu-Guang Zhong ◽  
Jian-Wei Ma
Keyword(s):  
High Efficiency ◽  
Cutting Tool ◽  
Joint Space ◽  
Cartesian Space ◽  
Feedrate Scheduling ◽  
Look Ahead ◽  
Scheduling Method ◽  
The Look ◽  
Current Interval ◽  
Five Axis

Scheduling of the five-axis spline toolpath feedrate is of great significance for high-quality and high-efficiency machining using five-axis machine tools. Due to the fact that there exists nonlinear relationship between the Cartesian space of the cutting tool and the joint space of the five feed axes, it is a challenging task to schedule the five-axis feedrate under axial drive constraints. Most existing methods are researched for routine short spline toolpaths, however, the five-axis feedrate scheduling method expressed for long spline toolpaths is limited. This article proposes an interval adaptive feedrate scheduling method based on a dynamic moving look-ahead window, so as to generate smooth feedrate for long five-axis toolpath in a piecewise manner without using the integral toolpath geometry. First, the length of the look-ahead window which equals to that of the toolpath interval is determined in case of abrupt braking at the end of the toolpath. Then, the interval permissible tangential feed parameters in terms of the velocity, acceleration, and jerk are determined according to the axial drive constraints at each toolpath interval. At the same time, the end velocity of the current interval is obtained through looking ahead the next interval. Using the start and end velocities and the permissible feed parameters of each interval, the five-axis motion feedrate is scheduled via an interval adaptive manner. Thus, the feedrate scheduling task for long five-axis toolpath is partitioned into a series of extremely short toolpaths, which realizes the efficient scheduling of long spline toolpath feedrate. Experimental results on two representative five-axis spline toolpaths demonstrate the feasibility of the proposed approach, especially for long toolpaths.

scholarly journals Research on Real-Time Joint Stiffness Configuration of a Series Parallel Hybrid 7-DOF Humanoid Manipulator in Continuous Motion

2021 ◽  
Vol 11 (5) ◽  
pp. 2433
Author(s):  
Yang Yu ◽  
Shimin Wei ◽  
Haiyan Sheng ◽  
Yingkun Zhang
Keyword(s):  
Real Time ◽  
Human Body ◽  
Joint Stiffness ◽  
Joint Space ◽  
Flexible Joints ◽  
Continuous Motion ◽  
The Real ◽  
Cartesian Space ◽  
Parallel Hybrid ◽  
The Relationship

In this paper, the real-time joint stiffness configuration strategy of a series parallel hybrid 7-DOF (degree of freedom) humanoid manipulator with flexible joints in continuous motion is studied. Firstly, considering the potential human robot accidental collision, combined with the manipulator safety index (MSI) and human body injury thresholds, the motion speed and joint stiffness of the robot are optimized in advance. Secondly, using hyperbolic tangent function for reference, the relationship between joint torques and passive joint deflection angles of the robot is given, which is beneficial for the real-time calculation of joint stiffness and obtain reasonable joint stiffness. Then, the structural model of the selected humanoid manipulator is described, on this basis, the relationship between the joint space stiffness and the Cartesian space stiffness of the humanoid manipulator is analyzed through Jacobian matrix, and the results show that the posture and joint space stiffness of the humanoid manipulator directly affect the Cartesian space stiffness of the humanoid manipulator. Finally, according to whether the humanoid manipulator works in the human-robot interaction environment, the real-time joint stiffness configuration of the humanoid manipulator in continuous motion is simulated and analyzed. The research shows that the humanoid manipulator with flexible joints can adjust the joint stiffness in real-time during continuous motion, and the joint stiffness configuration strategy can effectively improve the safety of human body in human-robot collision. In addition, in application, when the joint space stiffness of the robot is lower, the position accuracy can be improved by trajectory compensation.

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