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.

Kinematic Analysis of a Novel Three Degree of Freedom Parallel Mechanism

2011 ◽  
Vol 320 ◽  
pp. 228-231 ◽  
Author(s):  
Xiu Qin Huang ◽  
Hui Ping Shen ◽  
Xiu Mei Xin
Keyword(s):  
Industrial Application ◽  
Parallel Mechanism ◽  
Degree Of Freedom ◽  
Structural Parameter ◽  
Parallel Mechanisms ◽  
Input And Output ◽  
Solid Foundation ◽  
Input Variables ◽  
Three Degree Of Freedom ◽  
Kinematics Parameters

A novel 3 degree of freedom(1-Translation and 2-Rotation) parallel mechanisms is investigated. The forward and inverse position of the mechanism are studied. The influences by the three input variables on the three output variables are analyzed carefully and the valid working ranges of input and output variables are given by discussing structural parameter. These provide a solid foundation for selecting structural designs and kinematics parameters accurately and for realizing the control and industrial application of the mechanism.

Determination of the Singularity Loci of Spherical Three-Degree-of-Freedom Parallel Manipularors

1992 ◽  
Author(s):  
Clément M. Gosselin ◽  
Jaouad Sefrioui
Keyword(s):  
Graphical Representation ◽  
Jacobian Matrix ◽  
Parallel Manipulators ◽  
Degree Of Freedom ◽  
End Effector ◽  
Cartesian Space ◽  
Singularity Locus ◽  
Three Degree Of Freedom ◽  
Analytical Expressions

Abstract In this paper, an algorithm for the determination of the singularity loci of spherical three-degree-of-freedom parallel manipulators with prismatic atuators is presented. These singularity loci, which are obtained as curves or surfaces in the Cartesian space, are of great interest in the context of kinematic design. Indeed, it has been shown elsewhere that parallel manipulators lead to a special type of singularity which is located inside the Cartesian workspace and for which the end-effector becomes uncontrollable. It is therfore important to be able to identify the configurations associated with theses singularities. The algorithm presented is based on analytical expressions of the determinant of a Jacobian matrix, a quantity that is known to vanish in the singular configurations. A general spherical three-degree-of-freedom parallel manipulator with prismatic actuators is first studied. Then, several particular designs are investigated. For each case, an analytical expression of the singularity locus is derived. A graphical representation in the Cartesian space is then obtained.

The Mechanics of Parallel Mechanisms and Walking Machines

1994 ◽  
Vol 208 (6) ◽  
pp. 367-377 ◽  
Author(s):  
S J Zhang ◽  
D J Sanger ◽  
D Howard
Keyword(s):  
Parallel Mechanism ◽  
Virtual Work ◽  
The Body ◽  
Position Vector ◽  
Parallel Mechanisms ◽  
Active Joint ◽  
End Effector ◽  
Walking Machine ◽  
Walking Machines ◽  
Fixed Base

A parallel mechanism is one whose links and joints form two or more serially connected chains which join the fixed base and the end effector The mechanism of a multi-legged walking machine can be considered as a parallel mechanism whose base is not fixed and whose configuration changes during different phases of its gait. This paper presents methods for analysing the mechanics of parallel mechanisms and walking machines using vector and screw algebra Firstly, displacement analysis is covered; this includes general methods for deriving the position vector of any joint in any leg and for calculating the active joint displacements in any leg. Secondly, velocity analysis is covered which tackles the problem of calculating active joint velocities given the velocity, position and the orientation of the body and the positions of the feet. Thirdly, the static analysis of these classes of mechanisms using the principle of virtual work and screw algebra is given. Expressions are derived for the actuator forces and torques required to balance a given end effector (or body) wrench and, in the case of a walking machine, the ground reactions at the feet. Numerical examples are given to demonstrate the application of these methods.

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.

Novel Design and Analysis of a Fully Decoupled 3-DOF Spherical Parallel Robot

2009 ◽  
Author(s):  
Dan Zhang ◽  
Fan Zhang
Keyword(s):  
Physical Meaning ◽  
Parallel Mechanism ◽  
Jacobian Matrix ◽  
Parallel Robot ◽  
Degree Of Freedom ◽  
Redundant Constraints ◽  
Rotational Motions ◽  
Three Degree Of Freedom ◽  
Novel Design

In this paper, we propose a unique, decoupled Three Degree-of-Freedom (DOF) parallel wrist. The condition required for synthesizing a fully isotropic parallel mechanism is obtained based on the physical meaning of the row vector in the Jacobian Matrix. Specifically, an over-constrained spherical 3-DOF parallel mechanism is presented and the modified structure, which avoids the redundant constraints, is also introduced. The proposed manipulator is capable of decoupled rotational motions around the x, y and z axes and contains an output angle that is equal to the input angle. Since this device is analyzed with the Jacobian Matrix, which is constant, the mechanism is free of singularity and maintains homogenous stiffness over the entire workspace.

Effects of Three- or Four-Cortex Syndesmotic Fixation in Ankle Fractures

2007 ◽  
Vol 97 (6) ◽  
pp. 457-459 ◽  
Author(s):  
Hasan Karapinar ◽  
Onder Kalenderer ◽  
Levent Karapinar ◽  
Taskin Altay ◽  
Metin Manisali ◽  
...  
Keyword(s):  
Clinical Results ◽  
Joint Space ◽  
Ankle Fractures ◽  
Routine Procedure ◽  
Plain Radiographs ◽  
Weber Type ◽  
Type C ◽  
Type 3

Background: There is no study comparing how Weber type C ankle fractures treated with either three- or four-cortex syndesmotic fixation affects the structure of the syndesmosis. Methods: In a retrospective study, 46 patients were separated into two groups: 22 patients with three-cortex fixation and 24 patients with four-cortex fixation. All of the patients were evaluated clinically and radiographically at least 1 year after removal of the syndesmosis screws. Results: There were three types of joint space obliteration: type 1, synostosis on plain radiographs; type 2, an incomplete bony bridge on magnetic resonance imaging with normal plain radiographs; and type 3, fibrous obliteration of the joint space. Although obliteration of the joint space was significant (P < .005) after four-cortex fixation, radiologic results did not affect the clinical outcome. Conclusion: Four-cortex fixation for diastasis after an ankle fracture should not be a routine procedure. We advocate three-cortex fixation because the clinical results are no different and there is less syndesmotic space obliteration postoperatively. (J Am Podiatr Med Assoc 97(6): 457–459, 2007)

Synthesis, Design, and Prototyping of a Planar Three Degree-of-Freedom Reactionless Parallel Mechanism

2004 ◽  
Vol 126 (6) ◽  
pp. 992-999 ◽  
Author(s):  
Simon Foucault ◽  
Cle´ment M. Gosselin
Keyword(s):  
Parallel Mechanism ◽  
Degree Of Freedom ◽  
Numerical Verification ◽  
Dynamic Balancing ◽  
Synthesis Design ◽  
Reaction Forces ◽  
Three Degree Of Freedom

This paper addresses the dynamic balancing of a planar three-degree-of-freedom parallel mechanism. A mechanism is said to be dynamically balanced if, for any motion of the mechanism, the reaction forces and torques at the base are identically equal to zero, at all times. The proposed mechanism is based on legs consisting of five-bar parallelogram linkages. The balancing equations are first obtained. Then, optimization is used in order to minimize the mass and inertia of the moving links. Finally, a numerical verification of the dynamic balancing is provided and the prototype is presented.

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