Time suboptimal control of industrial manipulators along specified paths while keeping an end-effector orientation unchanged

Robotica ◽  
2003 ◽  
Vol 21 (2) ◽  
pp. 153-161 ◽  
Author(s):  
S. Kilicaslan ◽  
Y. Ercan
Keyword(s):  
Suboptimal Control ◽  
Time Step ◽  
End Effector ◽  
Industrial Manipulator ◽  
Industrial Manipulators ◽  
Angular Velocities ◽  
System Equations ◽  
Six Degree Of Freedom ◽  
Time Suboptimal Control

A method for the time suboptimal control of an industrial manipulator that moves along a specified path while keeping its end-effector orientation unchanged is proposed. Nonlinear system equations that describe the manipulator motion are linearized at each time step along the path. A method which gives control inputs (joint angular velocities) for time suboptimal control of the manipulator is developed. In the formulation, joint angular velocity and acceleration limitations are also taken into consideration. A six degree of freedom elbow type manipulator is used in a case study to verify the method developed.

Complete Accessibility of Oscillations in Robotic Systems by Orthogonal Projections

1990 ◽  
Vol 112 (2) ◽  
pp. 194-202 ◽  
Author(s):  
Sabri Tosunoglu ◽  
Shyng-Her Lin ◽  
Delbert Tesar
Keyword(s):  
Current Practice ◽  
Industrial Robot ◽  
Robotic Systems ◽  
Orthogonal Projections ◽  
Small Oscillations ◽  
Robotic Arms ◽  
Driven System ◽  
System Equations ◽  
Six Degree Of Freedom

The current practice of controller development for flexible robotic systems generally focuses on one-link robotic arms and is valid for small oscillations. This work addresses the control of n-link, serial, spatial robotic systems modeled with m1 joint and m2 link flexibilities such that n≥m1+m2. System compliance is modeled by local springs and nonactuated prismatic and revolute type pseudo joints. The coupled, nonlinear, error-driven system equations are derived for the complete model without linearization or neglecting certain terms. For this system, the complete accessibility of vibrations is studied by orthogonal projections. It is shown that under some configurations of a robotic system, the induced oscillations may not be accessible to the controller. Given accessibility, the controller developed in this work assures the global asymptotic stability of the system. Example numerical simulations are presented based on the model of a six-degree-of-freedom Cincinnati Milacron T3-776 industrial robot. One example models the system compliance in four joints, while another case study simulates four lateral link oscillations. These examples show that this controller, even under inaccurate payload description, eliminates the oscillations while tracking desired trajectories.

Improvement of the Accuracy of a PUMA 560 Industrial Manipulator by Calibration

1996 ◽  
Vol 210 (1) ◽  
pp. 55-67
Author(s):  
A R Greig ◽  
S P Lovell
Keyword(s):  
Supervisory Control ◽  
Joint Angle ◽  
Correction Function ◽  
Positional Accuracy ◽  
End Effector ◽  
Industrial Manipulator ◽  
Angle Measurements ◽  
Point Analysis ◽  
Industrial Manipulators ◽  
Data Points

Compared to their repeatability, the accuracy of industrial manipulators is disappointingly poor. To permit off-line programming of manipulators and interaction with their local surrounds a high positional accuracy is required; this is particularly true for operation under supervisory control. The accuracy of a manipulator can be improved by calibration of its link lengths and joint angle measurements. This paper presents the results of the calibration of a PUMA 560 industrial manipulator and discusses simplifications to the procedure and theory which improve the practicality of the method without seriously compromising the results. Circle point analysis is used with data points being recorded by a pair of theodolites; the relevant theory is presented in the Appendix. A joint error correction function is produced for each joint. A fourfold improvement in accuracy is demonstrated without unduly increasing the complexity of the kinematics or requiring a sophisticated end effector.

A Low-Cost Hexa Platform for Efficient Force Control Systems Using Industrial Manipulators

2009 ◽  
Vol 147-149 ◽  
pp. 1-6 ◽  
Author(s):  
Rafal Osypiuk ◽  
Torsten Kröger
Keyword(s):  
Control Systems ◽  
Force Control ◽  
Execution Time ◽  
Low Cost ◽  
Degree Of Freedom ◽  
Industrial Manipulators ◽  
Control Concept ◽  
Six Dof ◽  
Parallel Platform ◽  
Six Degree Of Freedom

This contribution presents a new force control concept for industrial six-degree of freedom (DOF) manipulators, which uses a Hexa platform that provides an active environmental stiffness for all six DOFs. The paper focuses on the Hexa platform and is split into two essential parts: (i) parallel platform construction, and (ii) application of force control with industrial manipulators using a six-DOF environmental stiffness. This mechatronic solution almost gives one hundred percent robustness for stiffness changes in the environment, what guaranties a significant shortening of execution time.

Parameterization of Three-Dimensional Rigid Body Guidance Incorporating Planar Gear Connections in a Spatial Closed-Loop Mechanism With Parallel Consecutive Axes

2008 ◽  
Author(s):  
Javier Rolda´n Mckinley ◽  
Carl Crane ◽  
David B. Dooner
Keyword(s):  
Computer Animation ◽  
Closed Loop ◽  
Three Dimensional ◽  
Motion Generation ◽  
Repetitive Motion ◽  
End Effector ◽  
Spatial Mechanism ◽  
Joint Axis ◽  
Position And Orientation ◽  
Six Degree Of Freedom

This paper introduces a reconfigurable closed-loop spatial mechanism that can be applied to repetitive motion tasks. The concept is to incorporate five pairs of non-circular gears into a six degree-of–freedom closed-loop spatial chain. The gear pairs are designed based on given mechanism parameters and a user defined motion specification of a coupler link of the mechanism. It is shown in the paper that planar gear pairs can be used if the spatial closed-loop chain is comprised of six pairs of parallel joint axes, i.e. the first joint axis is parallel to the second, the third is parallel to the fourth, ..., and the eleventh is parallel to the twelfth. This paper presents the synthesis of the gear pairs that satisfy a specified three-dimensional position and orientation need. Numerical approximations were used in the synthesis the non-circular gear pairs by introducing an auxiliary monotonic parameter associated to each end-effector position to parameterize the motion needs. The findings are supported by a computer animation. No previous known literature incorporates planar non-circular gears to fulfill spatial motion generation needs.

scholarly journals Metaheuristic techniques comparison to optimize robotic end-effector behavior and its workspace

2018 ◽  
Vol 15 (5) ◽  
pp. 172988141880113
Author(s):  
Miguel Angel Funes Lora ◽  
Edgar Alfredo Portilla-Flores ◽  
Raul Rivera Blas ◽  
Emmanuel Alejandro Merchán Cruz ◽  
Manuel Faraón Carbajal Romero
Keyword(s):  
Numerical Technique ◽  
Cuckoo Search ◽  
Optimization Methods ◽  
Metaheuristic Algorithms ◽  
End Effector ◽  
Bee Colony ◽  
Ill Posed ◽  
Metaheuristic Techniques

Many robots are dedicated to replicate trajectories recorded manually; the recorded trajectories may contain singularities, which occur when positions and/or orientations are not achievable by the robot. The optimization of those trajectories is a complex issue and classical optimization methods present a deficient performance when solving them. Metaheuristics are well-known methodologies for solving hard engineering problems. In this case, they are applied to obtain alternative trajectories that pass as closely as possible to the original one, reorienting the end-effector and displacing its position to avoid the singularities caused by limitations of inverse kinematics equations, the task, and the workspace. In this article, alternative solutions for an ill-posed problem concerning the behavior of the robotic end-effector position and orientation are proposed using metaheuristic algorithms such as cuckoo search, differential evolution, and modified artificial bee colony. The case study for this work considers a three-revolute robot (3R), whose trajectories can contain or not singularities, and an optimization problem is defined to minimize the objective function that represents the error of the alternative trajectories. A tournament in combination with a constant of proportionality allows the metaheuristics to modify the gradual orientation and position of the robot when a singularity is present. Consequently, the procedure selects from all the possible elbow-configurations the best that fits the trajectory. A classical numerical technique, Newton’s method, is used to compare the results of the applied metaheuristics, to evaluate their quality. The results of this implementation indicate that metaheuristic algorithms are an efficient tool to solve the problem of optimizing the end-effector behavior, because of the quality of the alternative trajectory produced.

scholarly journals A singularity handling algorithm based on operational space control for six-degree-of-freedom anthropomorphic manipulators

2019 ◽  
Vol 16 (3) ◽  
pp. 172988141985891
Author(s):  
Zhi-Hao Kang ◽  
Ching-An Cheng ◽  
Han-Pang Huang
Keyword(s):  
Null Space ◽  
Singularity Analysis ◽  
Degree Of Freedom ◽  
Control Input ◽  
Real Time Control ◽  
Time Control ◽  
Operational Space ◽  
Industrial Manipulators ◽  
Space Motion ◽  
Six Degree Of Freedom

In this article, we analyze the singularities of six-degree-of-freedom anthropomorphic manipulators and design a singularity handling algorithm that can smoothly go through singular regions. We show that the boundary singularity and the internal singularity points of six-degree-of-freedom anthropomorphic manipulators can be identified through a singularity analysis, although they do not possess the nice kinematic decoupling property as six-degree-of-freedom industrial manipulators. Based on this discovery, our algorithm adopts a switching strategy to handle these two cases. For boundary singularities, the algorithm modifies the control input to fold the manipulator back from the singular straight posture. For internal singularities, the algorithm controls the manipulator with null space motion. We show that this strategy allows a manipulator to move within singular regions and back to non-singular regions, so the usable workspace is increased compared with conventional approaches. The proposed algorithm is validated in simulations and real-time control experiments.

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