Uncertainty Problems in Model-Based Control of Redundantly Actuated Parallel Manipulators

2008 ◽  
Author(s):  
Andreas Mu¨ller
Keyword(s):  
Inverse Dynamics ◽  
Closed Form Solution ◽  
Parallel Manipulators ◽  
Form Solution ◽  
Torque Control ◽  
Secondary Tasks ◽  
Control Schemes ◽  
Dynamics And Control ◽  
Redundantly Actuated ◽  
Control Forces

The inverse dynamics and control of redundantly actuated PKM in the presence of uncertainties is the focus of this paper. Actuation redundancy allows for a purposeful distribution of control forces, taking into account secondary tasks, such optimal force distribution, active stiffness, and backlash avoiding control. A closed form solution of the inverse dynamics problem for simply redundantly actuated PKM is given. The applicability of the augmented PD and computed torque control schemes is analyzed. It is shown that, in the presence of model uncertainties, adopting the standard control schemes leads to parasitic perturbation forces that can not be compensated by the controls. An amended version of these control scheme is proposed that does not suffer from such effects.

Adaptive and Singularity-Free Inverse Dynamics Models for Control of Parallel Manipulators With Actuation Redundancy

2011 ◽  
Author(s):  
Andreas Mu¨ller ◽  
Timo Hufnagel
Keyword(s):  
Range Of Motion ◽  
Inverse Dynamics ◽  
Null Space ◽  
Parallel Manipulators ◽  
Point Of View ◽  
Torque Control ◽  
Alternative Formulation ◽  
Dynamics Model ◽  
Model Based ◽  
Control Forces

Redundant actuation of parallel kinematics machines (PKM) is a way to eliminate input-singularities and so to enlarge the usable workspace. From a kinematic point of view the number m of actuator coordinates exceeds the DOF δ of a redundantly actuated PKM (RA-PKM). The dynamics model, being the basis for model-based control, is usually expressed in terms of δ independent actuator coordinates. This implies that the model exhibits the same singularities as the non-redundant PKM, even though the RA-PKM is not singular. Consequently the admissible range of motion of the RA-PKM model is limited to that of the non-redundant PKM. In this paper an alternative formulation of the dynamics model in terms of the full set of m actuator coordinates is presented. It leads to a redundant system of m motion equations that is valid in the entire range of motion. This formulation gives rise to an inverse dynamics formulation tailored for real-time implementation. In contrast to the standard formulation in independent coordinates, the proposed inverse dynamics formulation does not involve control forces in the null space of the control matrix, i.e. it does not allow for the generation of internal prestresses, however. This is not problematic as the latter is usually not exploited. The proposed method is compared to the recently proposed adaptive coordinate switching method. Experimental results are reported if the inverse dynamics solution is introduced in model-based computed torque control scheme of a planar 2DOF RA-PKM.

A note on the inverse dynamic control of parallel manipulators

2009 ◽  
Vol 224 (1) ◽  
pp. 25-32 ◽  
Author(s):  
A Omran ◽  
M Elshabasy
Keyword(s):  
Inverse Dynamics ◽  
Dynamic Control ◽  
Closed Form Solution ◽  
Parallel Manipulators ◽  
Joint Space ◽  
Form Solution ◽  
Control Technique ◽  
Inverse Dynamic ◽  
Inverse Dynamics Control ◽  
Inverse Dynamic Control

This work proposes a simple technique for inverse dynamics control of parallel mani-pulators in a joint space. In this technique, there is no need for forward kinematics, which is exacerbated by no closed-form solution for many parallel manipulators. A set of simulations is introduced to signify the validity of the proposed control technique compared with full joint feedback control.

scholarly journals Mobility analysis of a robotic cardiopulmonary resuscitation device

2021 ◽  
Author(s):  
Mahdi Ardestani ◽  
Mohsen Asgari
Keyword(s):  
Parallel Mechanism ◽  
Jacobian Matrix ◽  
Closed Form Solution ◽  
Parallel Manipulators ◽  
Optimization Method ◽  
Form Solution ◽  
Mobility Analysis ◽  
Chest Compressions ◽  
Singularity Problem ◽  
Lower Mobility

Abstract During chest compressions action, in CPR (CPR), the 2 arms of the rescuer constitute a parallel mechanism. Inspired by this performance, during this study a specific family of lower mobility parallel manipulators by employing a modified version of Delta robot is proposed for chest compressions in rescuing a patient. One of the biggest differences between this mechanism and the Delta parallel mechanism is that the position of the three active connections of the robot relative to each other has changed the geometry of the platforms. Also, it shapes the asymmetrical structure within the robot mechanism and its workspace. Another difference is due to the architectural optimization method considering the mixed performance index, which has been used during this mechanism to achieve a much better compromise between the manipulator dexterity and its workspace. Within the present paper, after introducing the architecture of the robot, a closed-form solution is developed for the kinematic problem and therefore the results are verified using MSC. Adams©. Then Jacobian matrix is generated to gauge the singularity problem of the proposed mechanism. then, the workspace of the robot is investigated and compared with the original Delta mechanism.

Closed form solution to the position workspace of Stewart parallel manipulators

1998 ◽  
Vol 41 (4) ◽  
pp. 393-403 ◽  
Author(s):  
Tian Huang ◽  
Jinsong Wang ◽  
D. J. Whitehouse
Keyword(s):  
Closed Form ◽  
Closed Form Solution ◽  
Parallel Manipulators ◽  
Form Solution

scholarly journals PSO-Based Soft Lunar Landing with Hazard Avoidance: Analysis and Experimentation

Aerospace ◽  
2021 ◽  
Vol 8 (7) ◽  
pp. 195
Author(s):  
Andrea D’Ambrosio ◽  
Andrea Carbone ◽  
Dario Spiller ◽  
Fabio Curti
Keyword(s):  
Real Time ◽  
Inverse Dynamics ◽  
A Priori ◽  
Closed Form Solution ◽  
Control Policy ◽  
Form Solution ◽  
Soft Landing ◽  
Lunar Landing ◽  
Optimal Guidance ◽  
Time Optimal

The problem of real-time optimal guidance is extremely important for successful autonomous missions. In this paper, the last phases of autonomous lunar landing trajectories are addressed. The proposed guidance is based on the Particle Swarm Optimization, and the differential flatness approach, which is a subclass of the inverse dynamics technique. The trajectory is approximated by polynomials and the control policy is obtained in an analytical closed form solution, where boundary and dynamical constraints are a priori satisfied. Although this procedure leads to sub-optimal solutions, it results in beng fast and thus potentially suitable to be used for real-time purposes. Moreover, the presence of craters on the lunar terrain is considered; therefore, hazard detection and avoidance are also carried out. The proposed guidance is tested by Monte Carlo simulations to evaluate its performances and a robust procedure, made up of safe additional maneuvers, is introduced to counteract optimization failures and achieve soft landing. Finally, the whole procedure is tested through an experimental facility, consisting of a robotic manipulator, equipped with a camera, and a simulated lunar terrain. The results show the efficiency and reliability of the proposed guidance and its possible use for real-time sub-optimal trajectory generation within laboratory applications.

On the Control of Tendon Based Parallel Manipulators

2010 ◽  
Vol 166-167 ◽  
pp. 395-402
Author(s):  
Christian Sturm ◽  
Dieter Schramm
Keyword(s):  
Direct Contact ◽  
High Speed ◽  
Inverse Dynamics ◽  
Parallel Manipulators ◽  
Operational Space ◽  
Control Scheme ◽  
Control Schemes ◽  
Environment Control ◽  
Internal Forces ◽  
External Forces

Tendon based parallel manipulators are capable of realizing movement of high speed and acceleration. In order to perform tasks that require direct contact with the environment control schemes are needed that adapt both operational space variables and tendon forces. By use of an inverse dynamics approach a motion control scheme in operational space is presented. In redundant systems the forces that act along the tendons can be divided into internal forces, the sum of which is zero, and external forces, that produce the driving force for the endeffector. Based on that property an additional and decoupled force control scheme is presented.

Orientation Workspace and Stiffness Optimization of Cable-Driven Parallel Manipulators With Base Mobility

2017 ◽  
Vol 9 (3) ◽  
Author(s):  
Michael Anson ◽  
Aliakbar Alamdari ◽  
Venkat Krovi
Keyword(s):  
Closed Form Solution ◽  
Parallel Manipulators ◽  
Form Solution ◽  
Base System ◽  
Advantages And Disadvantages ◽  
Symmetric Configuration ◽  
Circular Configuration ◽  
Rectangular Configuration ◽  
Orientation Workspace

Cable-driven parallel manipulators (CDPM) potentially offer many advantages over serial manipulators, including greater structural rigidity, greater accuracy, and higher payload-to-weight ratios. However, CDPMs possess limited moment resisting/exerting capabilities and relatively small orientation workspaces. Various methods have been contemplated for overcoming these limitations, each with its own advantages and disadvantages. The focus of this paper is on one such method: the addition of base mobility to the system. Such base mobility gives rise to kinematic redundancy, which needs to be resolved carefully in order to control the system. However, this redundancy can also be exploited in order to optimize some secondary criteria, e.g., maximizing the size and quality of the wrench-closure workspace with the addition of base mobility. In this work, the quality of the wrench-closure workspace is examined using a tension-factor index. Two planar mobile base configurations are investigated, and their results are compared with a traditional fixed-base system. In the rectangular configuration, each base is constrained to move along its own linear rail, with each rail forming right angles with the two adjacent rails. In the circular configuration, the bases are constrained to move along one circular rail. While a rectangular configuration enhances the size and quality of the orientation workspace in a particular rotational direction, the circular configuration allows for the platform to obtain any position and orientation within the boundary of the base circle. Furthermore, if the bases are configured in such a way that the cables are fully symmetric with respect to the platform, a maximum possible tension-factor of one is guaranteed. This fully symmetric configuration is shown to offer a variety of additional advantages: it eliminates the need to perform computationally expensive nonlinear optimization by providing a closed-form solution to the inverse kinematics problem, and it results in a convergence between kinematic singularities and wrench-closure singularities of the system. Finally, we discuss a particular limitation of this fully symmetric configuration: the inability of the cables to obtain an even tension distribution in a loaded configuration. For this reason, it may be useful to relax the fully symmetric cable requirement in order to yield reasonable tensions of equal magnitude.

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