Singular Assembly Configurations and Configuration Bifurcation Characteristics of the SRHGSMP

2008 ◽  
Author(s):  
Yu-Xin Wang ◽  
Yu-Tong Li ◽  
Zheng Huang ◽  
Shuang-Xia Pian
Keyword(s):  
Motion Control ◽  
Parallel Manipulator ◽  
Jacobian Matrix ◽  
Singular Points ◽  
The Self ◽  
Trajectory Design ◽  
Singularity Avoidance ◽  
Input Parameters ◽  
Matrix Correlation ◽  
Self Motion

In this paper, the configuration bifurcation characteristics at the vicinities of singular points going with different input parameters are investigated. Then, with the aid of the assembly configurations at the theoretical singular points, the reasons to cause the singularities are analyzed. We find that the dimensional-utmost singularities, line vectors correlation singularities and Jacobian matrix correlation singularities can occur individually or jointly while choosing different number of input parameters. The number and the combination form of the input parameters have great influences on the complexity of the singularities and the curvature radiuses of the configuration curves. Selecting a group of adjacent input parameters, the simple configuration bifurcation and the large singularity-free input parameters zones can be obtained. And adopting multi-input parameters, the self-motion regions and the singularity avoidance errors can be reduced. These new discoveries are valuable and of significance for the trajectory design, the singularity avoidance, and the self-motion control for the parallel manipulator, as well as the parallel tools.

Maximal singularity-free distribution of input parameters in a parallel manipulator considering load deformations and clearances

2010 ◽  
Vol 225 (1) ◽  
pp. 204-215 ◽  
Author(s):  
Y-T Li ◽  
Y Hong ◽  
Y-X Wang ◽  
T-Y Li ◽  
G-D Wang
Keyword(s):  
Parallel Manipulator ◽  
Parallel Manipulators ◽  
Singular Points ◽  
Design Stage ◽  
Early Design Stage ◽  
Free Distribution ◽  
Maximal Singularity ◽  
Input Parameters ◽  
Singularity Distribution ◽  
External Loads

It is well known that singularities are inherent to parallel manipulators and have serious influence on their properties. It is desired that the motion uncertainty caused by the singularity should be avoided in the design and operation stages. The singularity distribution hypersurface shows the relations among the pose components at the singular points, but it is difficult to be utilized in predicting the motion certainty through checking and controlling the lengths of input parameters. In this article, taking a 3-RPR parallel manipulator as an example, and considering the clearances existing in the joints and the deformations of the input actuating cylinders under external loads, the maximal singularity-free distribution of input parameters is investigated. While the input parameters are located within the space enveloped by the maximal singularity-free distribution surfaces, the manipulator can bear the required external loads and give out a certain motion at the neighbourhood of singular points. Based on this kind of the maximal singularity-free distribution of input parameters, the singularity can be avoided both in the early design stage by assigning the input parameters into a suitable region and in the operation state through controlling and monitoring the values of the input parameters.

Study on the method for 6-SPS Gough—Stewart platforms to pass through type-II singular points with its original configuration

2008 ◽  
Vol 222 (4) ◽  
pp. 723-736 ◽  
Author(s):  
Yu-X Wang ◽  
Y-T Li ◽  
R-Q Guo
Keyword(s):  
Parallel Manipulator ◽  
Turning Point ◽  
Parallel Manipulators ◽  
Singular Points ◽  
The Other ◽  
Type Ii ◽  
Input Parameters ◽  
Novel Method ◽  
Pass Through ◽  
Original Configuration

It is well known that there exist many more singularities in parallel manipulators. At the singular point, the motion of the parallel manipulator is uncertain. In order to make parallel manipulators produce concrete output at singular points, and go away from singular points with the desired configuration, the method for the manipulator to pass through type-II singularities with its original configuration has been investigated in the paper. First, the semi-regular hexagon Gough—Stewart manipulator is taken as an example to analyse the configuration bifurcation characteristics at the vicinities of the type-II singularities going with the input parameters. The studies show that on different configuration branches, the singularity-free moving region is different, and there are two or four assembly configurations in the space above the base for the same group of input parameters. By researching transition behaviours of the configuration bifurcation curves under the disturbances applied to the other input parameters, it is found that under a suitable disturbance the perturbed persistent configuration will go away from the non-persistent configuration. Based on this kind of character, a novel method for the manipulator to pass through the turning point with its original configuration has been presented.

Design and analysis of CICABOT: a novel translational parallel manipulator based on two 5-bar mechanisms

Robotica ◽  
2011 ◽  
Vol 30 (3) ◽  
pp. 449-456 ◽  
Author(s):  
M. F. Ruiz-Torres ◽  
E. Castillo-Castaneda ◽  
J. A. Briones-Leon
Keyword(s):  
Parallel Manipulator ◽  
Jacobian Matrix ◽  
Geometric Analysis ◽  
Vector Equation ◽  
Prismatic Joints ◽  
Hollow Cylinders ◽  
Moving Platform ◽  
Direct Kinematics

SUMMARYThis work presents the CICABOT, a novel 3-DOF translational parallel manipulator (TPM) with large workspace. The manipulator consists of two 5-bar mechanisms connected by two prismatic joints; the moving platform is on the union of these prismatic joints; each 5-bar mechanism has two legs. The mobility of the proposed mechanism, based on Gogu approach, is also presented. The inverse and direct kinematics are solved from geometric analysis. The manipulator's Jacobian is developed from the vector equation of the robot legs; the singularities can be easily derived from Jacobian matrix. The manipulator workspace is determined from analysis of a 5-bar mechanism; the resulting workspace is the intersection of two hollow cylinders that is much larger than other TPM with similar dimensions.

Jacobian Analysis of a Fully Decoupled Parallel Manipulator for Minimally Invasive Surgery

2012 ◽  
Author(s):  
Chin-Hsing Kuo ◽  
Jian S. Dai
Keyword(s):  
Minimally Invasive Surgery ◽  
Minimally Invasive ◽  
Invasive Surgery ◽  
Parallel Manipulator ◽  
Jacobian Matrix ◽  
Central Point ◽  
Special Structure ◽  
Jacobian Matrices ◽  
Singular Configurations ◽  
Reachable Workspace

This paper presents the Jacobian analysis of a parallel manipulator that has a fully decoupled 4-DOF remote center-of-motion for application in minimally invasive surgery. Owing to the special structure of the manipulator, the Jacobian matrix of the manipulator is expressed as a combination of three special Jacobian matrices, namely the Jacobian of motion space, Jacobian of constraints, and Jacobian of actuations. Based on these Jacobian matrices, the singular configurations of the manipulator are then identified. It shows that the configuration singularity only exists at the central point and the boundary of the reachable workspace of the manipulator.

Dynamic Modeling of a Parallel Manipulator With Three Translational Degrees of Freedom

1998 ◽  
Author(s):  
Richard Stamper ◽  
Lung-Wen Tsai
Keyword(s):  
Parallel Manipulator ◽  
Degrees Of Freedom ◽  
Close Agreement ◽  
Jacobian Matrix ◽  
Parallel Manipulators ◽  
Kinematic Structure ◽  
End Effector ◽  
Moving Platform ◽  
Euler Approach ◽  
Computationally Intensive

Abstract The dynamics of a parallel manipulator with three translational degrees of freedom are considered. Two models are developed to characterize the dynamics of the manipulator. The first is a traditional Lagrangian based model, and is presented to provide a basis of comparison for the second approach. The second model is based on a simplified Newton-Euler formulation. This method takes advantage of the kinematic structure of this type of parallel manipulator that allows the actuators to be mounted directly on the base. Accordingly, the dynamics of the manipulator is dominated by the mass of the moving platform, end-effector, and payload rather than the mass of the actuators. This paper suggests a new method to approach the dynamics of parallel manipulators that takes advantage of this characteristic. Using this method the forces that define the motion of moving platform are mapped to the actuators using the Jacobian matrix, allowing a simplified Newton-Euler approach to be applied. This second method offers the advantage of characterizing the dynamics of the manipulator nearly as well as the Lagrangian approach while being less computationally intensive. A numerical example is presented to illustrate the close agreement between the two models.

The directions of nystagmus and apparent self-motion evoked by caloric tests and angular accelerations

2002 ◽  
Vol 11 (6) ◽  
pp. 349-355
Author(s):  
Ognyan I. Kolev
Keyword(s):  
Motion Perception ◽  
Frontal Plane ◽  
Vertical Axis ◽  
The Body ◽  
The Self ◽  
Whole Body ◽  
Caloric Stimulation ◽  
Infrared Video ◽  
Axis Rotation ◽  
Self Motion

Purpose: To further investigate the direction of (I) nystagmus and (II) self-motion perception induced by two stimuli: (a) caloric vestibular stimulations and (b) a sudden halt during vertical axis rotation. Subjects and methods: Twelve normal humans received caloric stimulation at 44°C, 30°C, and 20°C while in a supine position with the head inclined 30° upwards. In a second test they were rotated around the vertical axis with the head randomly placed in two positions: tilted 30° forward or tilted 60° backward, at a constant velocity of 90°/sec for 2 minutes and then suddenly stopped. After both tests they were asked to describe their sensations of self-motion. Eye movements were recorded with an infrared video-technique. Results: Caloric stimulation evoked only horizontal nystagmus in all subjects and induced a non-uniform complex perception of angular in frontal and transverse planes (the former dominated) and linear movements along the antero-posterior axis (sinking dominated) of the subject's coordinates. The self-motion was felt with the whole body or with a part of the body. Generally the perception evoked by cold (30°C) and warm (44°C) calorics was similar, although there were some differences. The stronger stimulus (20°C) evoked not only quantitative but also qualitative differences in perception. The abrupt halt of rotation induced self-motion perception and nystagmus only in the plane of rotation. The self-motion was felt with the whole body. Conclusion: There was no difference in the nystagmus evoked by caloric stimulation and a sudden halt of vertical axis rotation (in head positions to stimulate the horizontal canals); however, the two stimuli evoked different perceptions of self-motion. Calorics provoked the sensation of self-rotation in the frontal plane and linear motion, which did not correspond to the direction of nystagmus, as well as arcing and a reset phenomenon during angular and linear self-motion, caloric-induced self-motion can be felt predominantly or only with a part of the body, depending on the self-motion intensity. The findings indicate that, unlike the self-motion induced by sudden halt of vertical axis rotation, several mechanisms take part in generating caloric-induced self-motion.

Path Tracking of Parallel Manipulators in the Presence of Force Singularity

2005 ◽  
Vol 127 (4) ◽  
pp. 550-563 ◽  
Author(s):  
C. K. Kevin Jui ◽  
Qiao Sun
Keyword(s):  
Motion Planning ◽  
Parallel Manipulator ◽  
Inverse Dynamics ◽  
Parallel Manipulators ◽  
Path Tracking ◽  
Singularity Avoidance ◽  
Design Complexity ◽  
Actuation Redundancy ◽  
Planar Parallel Manipulator ◽  
Simulation Results

Parallel manipulators are uncontrollable at force singularities due to the infeasibly high actuator forces required. Existing remedies include the application of actuation redundancy and motion planning for singularity avoidance. While actuation redundancy increases cost and design complexity, singularity avoidance reduces the effective workspace of a parallel manipulator. This article presents a path tracking type of approach to operate parallel manipulators when passing through force singularities. We study motion feasibility in the neighborhood of singularity and conclude that a parallel manipulator may track a path through singular poses if its velocity and acceleration are properly constrained. Techniques for path verification and tracking are presented, and an inverse dynamics algorithm that takes actuator bounds into account is examined. Simulation results for a planar parallel manipulator are given to demonstrate the details of this approach.

The Breathing Light Illusion

2017 ◽  
Author(s):  
Simone Gori ◽  
Enrico Giora ◽  
D. Alan Stubbs
Keyword(s):  
The Self ◽  
White Spot ◽  
Physical Stimulus ◽  
Black Background ◽  
Static View ◽  
Self Motion

This chapter discusses the Breathing Light Illusion. The Breathing Light Illusion is a size and brightness illusion elicited by the self-motion of the observer. The stimulus consists of a circular white spot that is presented on a black background, characterized by blurred boundaries. The blurred spot, which in static view seems to glow and exhibits a self-luminance appearance, is perceived as wider, brighter, and more diffuse when it is approached but smaller, darker, and sharper when one recedes from it. A possible explanation of the phenomenon is related to the superimposition of the afterimage on the physical stimulus during dynamical viewing.

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