Disturbed Configuration Bifurcation Characteristics of Gough–Stewart Parallel Manipulators at Singular Points

2007 ◽  
Vol 130 (2) ◽  
Author(s):  
Yu-Xin Wang ◽  
Yu-Tong Li
Keyword(s):  
Parallel Manipulators ◽  
Singular Points ◽  
Unperturbed System ◽  
Rank Reduction ◽  
Universal Unfolding ◽  
Novel Approach ◽  
Parallel Machine Tools ◽  
Perturbation Parameters ◽  
Pass Through ◽  
Point Type

In this paper, the disturbed configuration bifurcation characteristics of Gough–Stewart parallel manipulators at singular points are investigated. At first, the expended equation corresponding with the kinematics equation of the manipulator is introduced for eliminating the rank reduction and obtaining all of the theoretical singular points. Then, the assembly configurations at the singular points and the configuration bifurcation characteristics near them have been studied. It is found that the configuration bifurcation characteristics at the singular points belong to the turning point type through the Golubitsky–Schaeffer normal form identification. Next, utilizing the universal unfolding approach, the configuration bifurcation characteristics under the perturbation parameters applied to the extendable legs are analyzed. The investigation reveals that all configuration branches converged in the same singular point in the unperturbed system will be separated in the disturbed system. Based on this discovery, a novel approach for the parallel manipulator to pass through the singular points with a desired configuration is presented. The method presented in this paper can be utilized as the singularity avoidance approach for the parallel manipulators with strict trace and exact orientation control requirements, such as virtual parallel machine tools.

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.

Singularity robust inverse dynamics of planar 2-RPR parallel manipulators

2004 ◽  
Vol 218 (7) ◽  
pp. 721-730 ◽  
Author(s):  
S Kemal Ider
Keyword(s):  
Parallel Manipulator ◽  
Inverse Dynamics ◽  
Full Rank ◽  
Parallel Manipulators ◽  
Parallel Robots ◽  
Dynamic Equations ◽  
Revolute Joints ◽  
Planar Parallel Manipulator ◽  
Pass Through ◽  
Full Utilization

In planar parallel robots, limitations occur in the functional workspace because of interference of the legs with each other and because of drive singularities where the actuators lose control of the moving platform and the actuator forces grow without bounds. A 2-RPR (revolute, prismatic, revolute joints) planar parallel manipulator with two legs that minimizes the interference of the mechanical components is considered. Avoidance of the drive singularities is in general not desirable since it reduces the functional workspace. An inverse dynamics algorithm with singularity robustness is formulated allowing full utilization of the workspace. It is shown that if the trajectory is planned to satisfy certain conditions related to the consistency of the dynamic equations, the manipulator can pass through the drive singularities while the actuator forces remain stable. Furthermore, for finding the actuator forces in the vicinity of the singular positions a full rank modification of the dynamic equations is developed. A deployment motion is analysed to illustrate the proposed approach.

scholarly journals A Novel Approach to Reduce the Unicast Bandwidth of an IPTV System in a High-Speed Access Network

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
El Hassane Khabbiza ◽  
Rachid El Alami ◽  
Hassan Qjidaa
Keyword(s):  
High Speed ◽  
Access Network ◽  
Channel Change ◽  
Set Top Box ◽  
Novel Approach ◽  
Assisted Delivery ◽  
High Bandwidth ◽  
Internet Protocol Television ◽  
Unicast Traffic ◽  
Pass Through

Channel change time is a critical quality of experience (QOE) metric for IP-based video delivery systems such as Internet Protocol Television (IPTV). An interesting channel change acceleration scheme based on peer-assisted delivery was recently proposed, which consists of deploying one FCC server (Fast Channel Change Server) in the IP backbone in order to send the unicast stream to the STB (Set-Top Box) before sending the normal multicast stream after each channel change. However, deploying such a solution will cause high bandwidth usage in the network because of the huge unicast traffic sent by the FCC server to the STBs. In this paper, we propose a new solution to reduce the bandwidth occupancy of the unicast traffic, by deploying the FCC server capabilities on the user STB. This means that, after each channel change request, the STB will receive the unicast traffic from another STB instead of the central server. By using this method, the unicast traffic will not pass through the IP network; it will be a peer-to-peer communication via the Access Network only. Extensive simulation results are presented to demonstrate the robustness of our new solution.

A Novel Method on Singularity Analysis in Parallel Manipulators

2006 ◽  
Author(s):  
Hodjat Pendar ◽  
Maryam Mahnama ◽  
Hassan Zohoor
Keyword(s):  
Closed Loop ◽  
Parallel Manipulators ◽  
Singularity Analysis ◽  
Parallel Mechanisms ◽  
Kinematic Chains ◽  
Working Space ◽  
Novel Approach ◽  
Main Technique ◽  
Novel Method ◽  
Constraint Plane

A parallel manipulator is a closed loop mechanism in which a moving platform is connected to the base by at least two serial kinematic chains. The main problem engaged in these mechanisms, is their restricted working space as a result of singularities. In order to tackle these problems, many methods have been introduced by scholars. However, most of the mentioned methods are too much time consuming and need a great amount of computations. They also in most cases do not provide a good insight to the existence of singularity for the designer. In this paper a novel approach is introduced and utilized to identify singularities in parallel manipulators. By applying the new method, one could get a better understanding of geometrical interpretation of singularities in parallel mechanisms. Here we have introduced the Constraint Plane Method (CPM) and some of its applications in parallel mechanisms. The main technique used here, is based on Ceva Theorem.

A Novel Approach to Kinematic Reliability Analysis for Planar Parallel Manipulators

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Qiangqiang Zhao ◽  
Junkang Guo ◽  
Dingtang Zhao ◽  
Dewen Yu ◽  
Jun Hong
Keyword(s):  
Reliability Analysis ◽  
Error Propagation ◽  
Simulation Method ◽  
Parallel Manipulators ◽  
Plane Motion ◽  
Error Sources ◽  
Novel Approach ◽  
Safe Region ◽  
Motion Groups ◽  
Planar Parallel Manipulators

Abstract Kinematic reliability is an essential index that assesses the performance of the mechanism associating with uncertainties. This study proposes a novel approach to kinematic reliability analysis for planar parallel manipulators based on error propagation on plane motion groups and clipped Gaussian in terms of joint clearance, input uncertainty, and manufacturing imperfection. First, the linear relationship between the local pose distortion coming from the passive joint and that caused by other error sources, which are all represented by the exponential coordinate, are established by means of the Baker–Campbell–Hausdorff formula. Then, the second-order nonparametric formulas of error propagation on independent and dependent plane motion groups are derived in closed form for analytically determining the mean and covariance of the pose error distribution of the end-effector. On this basis, the kinematic reliability, i.e., the probability of the pose error within the specified safe region, is evaluated by a fast algorithm. Compared to the previous methods, the proposed approach has a significantly high precision for both cases with small and large errors under small and large safe bounds, which is also very efficient. Additionally, it is available for arbitrarily distributed errors and can analyze the kinematic reliability only regarding either position or orientation as well. Finally, the effectiveness and advantages of the proposed approach are verified by comparing with the Monte Carlo simulation method.

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.

scholarly journals A Novel Approach for Detecting Rotational Angles of a Precision Spherical Joint Based on a Capacitive Sensor

Micromachines ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 280 ◽  
Author(s):  
Wen Wang ◽  
He Yang ◽  
Min Zhang ◽  
Zhanfeng Chen ◽  
Guang Shi ◽  
...  
Keyword(s):  
Real Time ◽  
Capacitive Sensor ◽  
Parallel Manipulators ◽  
Angle Measurement ◽  
Mechanical Transmission ◽  
Spherical Joint ◽  
Rotational Angle ◽  
Loop Control ◽  
Novel Approach ◽  
The Mathematical Model

Precision spherical joints are commonly employed as multiple degree-of-freedom (DOF) mechanical hinges in many engineering applications, e.g., robots and parallel manipulators. Real-time and precise measurement of the rotational angles of spherical joints is not only beneficial to the real-time and closed-loop control of mechanical transmission systems, but also is of great significance in the prediction and compensation of their motion errors. This work presents a novel approach for rotational angle measurement of spherical joints with a capacitive sensor. First, the 3-DOF angular motions of a spherical joint were analyzed. Then, the structure of the proposed capacitive sensor was presented, and the mathematical model for the rotational angles of a spherical joint and the capacitance of the capacitors was deduced. Finally, the capacitance values of the capacitors at different rotations were simulated using Ansoft Maxwell software. The simulation results show that the variation in the simulated capacitance values of the capacitors is similar to that of the theoretical values, suggesting the feasibility and effectiveness of the proposed capacitive detection method for rotational angles of spherical joints.

Configuration Bifurcation Characteristics of the Semi-Regular Hexagon Gough-Stewart Parallel Manipulator

2007 ◽  
Author(s):  
Yu-Xin Wang ◽  
Yu-Tong Li ◽  
Yi-Ming Wang ◽  
Xiu-Tian Yan
Keyword(s):  
Singular Point ◽  
Parallel Manipulator ◽  
Turning Point ◽  
Parallel Manipulators ◽  
Unperturbed System ◽  
Type Ii ◽  
Bifurcation Equation ◽  
One Dimensional ◽  
Perturbed System ◽  
Dimensional Equation

Type-II singularities exist in parallel manipulators commonly. At this kind of singularities, the end-effector is locally movable and uncertain even when all the actuate joints are located. In order to explore a possible approach to obtain the concrete output of the mobile platform at the very small vicinity (germ space) of the singular point, in this paper, the configuration bifurcation characteristics at the germ space have been investigated. At first, the type-II singularity has been identified with Golubitsky-Schaeffer normal form. The result shows that the type-II singular points belong to the turning points. Then, the configuration bifurcation equation is reduced into one dimensional form. Based on this one dimensional equation, the unperturbed and perturbed configuration bifurcation behaviors at the germ space of the turning point have been analyzed. It is found that all configuration branches converged in the same singular point in the unperturbed system can be separated in the perturbed system. This discovery has presented a possible approach to control the parallel manipulator passing through the singular point with a desired configuration.

scholarly journals Grasp planning for a reconfigurable parallel robot with an underactuated arm structure

2010 ◽  
Vol 1 (1) ◽  
pp. 33-42 ◽  
Author(s):  
M. Riedel ◽  
M. Nefzi ◽  
B. Corves
Keyword(s):  
Closed Loop ◽  
International Workshop ◽  
Parallel Manipulators ◽  
Parallel Robot ◽  
Grasp Planning ◽  
Robotic Arms ◽  
Cartesian Space ◽  
Novel Approach ◽  
Manipulation Task ◽  
Actuated Joints

Abstract. In this paper, a novel approach of grasp planning is applied to find out the appropriate grasp points for a reconfigurable parallel robot called PARAGRIP (Parallel Gripping). This new handling system is able to manipulate objects in the six-dimensional Cartesian space by several robotic arms using only six actuated joints. After grasping, the contact elements at the end of the underactuated arm mechanisms are connected to the object which forms a closed loop mechanism similar to the architecture of parallel manipulators. As the mounting and grasp points of the arms can easily be changed, the manipulator can be reconfigured to match the user's preferences and needs. This paper raises the question, how and where these grasp points are to be placed on the object to perform well for a certain manipulation task. This paper was presented at the IFToMM/ASME International Workshop on Underactuated Grasping (UG2010), 19 August 2010, Montréal, Canada.

Sign in / Sign up

Export Citation Format

Share Document