Singularities Classification for Structural Groups of Dyad Type

2014 ◽  
Vol 658 ◽  
pp. 47-54 ◽  
Author(s):  
Cezar Duca ◽  
Florentin Buium
Keyword(s):  
Closed Loop ◽  
Force Transmission ◽  
Structural Group ◽  
Planar Mechanisms ◽  
Singularity Problem ◽  
Transmission Quality

The paper deals with singularity problem of the closed-loop planar mechanisms. This problem is approached in addition with the force transmission quality in mechanism and mechanism self-locking. Another characteristic of this approach consist in the fact that it is based on the structural group notion. Taking into account its frequent usage in practice in the paper were treated only RRR, RRT and RTR structural groups.

Motion/Force Transmission Analysis of Parallel Mechanisms With Planar Closed-Loop Subchains

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
Kristan Marlow ◽  
Mats Isaksson ◽  
Jian S. Dai ◽  
Saeid Nahavandi
Keyword(s):  
Performance Measures ◽  
Parallel Mechanism ◽  
Degrees Of Freedom ◽  
Closed Loop ◽  
Screw Theory ◽  
Parallel Mechanisms ◽  
Force Transmission ◽  
Six Degrees Of Freedom ◽  
Lower Mobility ◽  
Transmission Ability

Singularities are one of the most important issues affecting the performance of parallel mechanisms. A parallel mechanism with less than six degrees of freedom (6DOF) is classed as having lower mobility. In addition to input–output singularities, such mechanisms potentially suffer from singularities among their constraints. Furthermore, the utilization of closed-loop subchains (CLSCs) may introduce additional singularities, which can strongly affect the motion/force transmission ability of the entire mechanism. In this paper, we propose a technique for the analysis of singularities occurring within planar CLSCs, along with a finite, dimensionless, frame invariant index, based on screw theory, for examining the closeness to these singularities. The integration of the proposed index with existing performance measures is discussed in detail and exemplified on a prototype industrial parallel mechanism.

Automatic Structural Synthesis of the Whole Family of Planar 3-Degrees of Freedom Closed Loop Mechanisms

2013 ◽  
Vol 5 (4) ◽  
Author(s):  
Huafeng Ding ◽  
Peng Huang ◽  
Jingfang Liu ◽  
Andrés Kecskeméthy
Keyword(s):  
Degrees Of Freedom ◽  
Closed Loop ◽  
Synthesis Method ◽  
Synthesis Process ◽  
Structural Synthesis ◽  
Planar Mechanisms ◽  
Systematic Method ◽  
Automatic Synthesis ◽  
Heavy Load ◽  
Structure Representation

Conception of the kinematic structures with better performance has been a challenging, yet pivotal issue, since the beginning of the design of mechanisms or robots. This paper proposes a systematic method to synthesize and classify automatically all the valid kinematic structures of planar 3-DOF closed loop mechanisms or robots. First, after the structure representation graphs of planar mechanisms or robots are addressed, the unique representation of both contracted graphs and topological graphs is proposed and used to detect isomorphism in the synthesis process. Then the valid atlas database of the contracted graphs for planar 3-DOF closed loop mechanisms or robots up to 16-link is built. Based on the atlas database, an automatic synthesis method is proposed to synthesize all the kinematic structures of planar 3-DOF closed loop mechanisms or robots, and the complete atlas database with all the valid kinematic structures classified for planar 3-DOF closed loop mechanisms or robots up to 16-link is established. The creative design of 3-DOF heavy-load hydraulic robots is conducted to show the usefulness of the established atlas database.

Statically Balanced Compliant Mechanisms (SBCM’S): An Example and Prospects

2000 ◽  
Author(s):  
Just L. Herder ◽  
Fred P. A. van den Berg
Keyword(s):  
Force Feedback ◽  
Compliant Mechanisms ◽  
Compensation Mechanism ◽  
Force Transmission ◽  
Low Friction ◽  
Transmission Process ◽  
Transmission Quality ◽  
Gripping Force ◽  
Elastic Elements

Abstract In some applications of compliant mechanisms, the fact that energy is stored in the elastic members presents a problem. For instance, in manually operated instruments, such as surgical forceps, the operating force should preferably be proportional to the gripping force, while forces introduced by the bending of elastic elements would disturb this force transmission process. To restore the force transmission quality, compliant mechanisms may be statically balanced, resulting in statically balanced compliant mechanisms (SBCM’s). This paper presents an example of a compliant surgical forceps mechanism, which is statically balanced by a low-friction rolling-link compensation mechanism. Force feedback is restored to the extent that the pulse in an artificial artery can be perceived clearly.

FORCE-AND-MOTION-TRANSMISSION EVALUATION IN SPATIAL MECHANISMS

2005 ◽  
Vol 29 (4) ◽  
pp. 527-539
Author(s):  
Chao Chen ◽  
Jorge Angeles
Keyword(s):  
Force Transmission ◽  
Pressure Angle ◽  
Spatial Mechanisms ◽  
Force And Motion ◽  
Transmission Index ◽  
Transmission Quality ◽  
Special Case

We propose a generalized transmission index for spatial mechanisms, based on the virtual coefficient between the transmission wrench screw and the output twist screw. Compared with other indices, ours is well defined in any case and able to evaluate the force transmission quality more precisely. We apply this index to mechanisms with higher pairs and show that the pressure angle is a special case of our index.

Motion/Force Transmission Analysis of Planar Parallel Mechanisms With Closed-Loop Subchains

2016 ◽  
Vol 8 (4) ◽  
Author(s):  
Kristan Marlow ◽  
Mats Isaksson ◽  
Saeid Nahavandi
Keyword(s):  
High Performance ◽  
Degrees Of Freedom ◽  
Closed Loop ◽  
Screw Theory ◽  
Parallel Mechanisms ◽  
Force Transmission ◽  
Transmission Performance ◽  
Specific Mechanism ◽  
Serial Chain ◽  
Four Bar Linkage

Singularities are one of the most important issues affecting the performance of parallel mechanisms. Therefore, analysis of their locations and closeness is essential for the development of a high-performance mechanism. The screw theory based motion/force transmission analysis provides such a closeness measure in terms of the work performed between specific mechanism twists and wrenches. As such, this technique has been applied to many serial chain parallel mechanisms. However, the motion/force transmission performance of parallel mechanisms with mixed topology chains is yet to be examined. These chains include linkages in both series and parallel, where the parallel portion is termed a closed-loop subchain (CLSC). This paper provides an analysis of such chains, where the CLSC is a planar four-bar linkage. In order to completely define the motion/force transmission abilities of these mechanisms, adapted wrench definitions are introduced. The proposed methodology is applied to a family of two degrees-of-freedom planar axis-symmetric parallel mechanisms, each with a different CLSC configuration. The presented analysis provides the first complete motion/force transmission analysis of such mechanisms.

Geometric design of planar mechanisms based on virtual guides for manipulation

Robotica ◽  
2015 ◽  
Vol 34 (12) ◽  
pp. 2653-2668 ◽  
Author(s):  
Nina Robson ◽  
Shramana Ghosh
Keyword(s):  
Rigid Body ◽  
Closed Loop ◽  
Normal Direction ◽  
Assistive Technologies ◽  
Paper Briefly ◽  
Planar Mechanisms ◽  
Kinematic Synthesis ◽  
Kinematic Chains ◽  
Moving Body ◽  
Mechanical Linkage

SUMMARYThis paper presents recent results and applications of our planar kinematic synthesis of serial and parallel linkages to guide a rigid body, such that it does not violate normal direction and curvature constraints imposed by contact with objects in the environment. The paper briefly reviews the recently developed theory on transforming contact direction and curvature constraints into conditions on velocity and acceleration of certain points in the moving body to obtain synthesis equations which can, subsequently be solved to find the dimensions of a mechanical linkage. The main contribution of the paper is in demonstrating the applicability of the proposed theory to the kinematic synthesis of both open and closed-loop kinematic linkages. We provide preliminary results on the synthesis of kinematic chains based on novel task specifications that incorporate curvature constraints with a variety of applications, such as passive suspensions for small rovers, assistive technologies, as well as grasping.

Approximated Grashof-Type Movability Conditions for RSSR Mechanisms With Force Transmission Limitations

1992 ◽  
Vol 114 (1) ◽  
pp. 74-81 ◽  
Author(s):  
J. Rastegar ◽  
Q. Tu
Keyword(s):  
Closed Form ◽  
Closed Loop ◽  
Open Loop ◽  
Approximation Technique ◽  
Force Transmission ◽  
Output Link ◽  
Link Type ◽  
Spatial Mechanisms ◽  
Loop Chain ◽  
Drag Link

Closed-form Grashof-type movability conditions are derived for closed-loop RSSR mechanisms using a geometrical approximation technique. The conditions that ensure the presence of crank-rocker and drag-link type mechanisms are derived with and without force transmission limitations. The force transmission limitations may be specified as a function of the output link angle. The accuracy of the approximated conditions is analyzed. As an example, the conditions are used to synthesize a function generating mechanism with fully rotatable crank and with various force transmission requirements. The developed technique is general, and can be applied to other similar spatial mechanisms. The application of this approach to geometrical synthesis of open-loop chain manipulators is discussed.

Adaptive H∞ Control Using Backstepping Design and Neural Networks

2004 ◽  
Vol 127 (3) ◽  
pp. 478-485 ◽  
Author(s):  
Yugang Niu ◽  
James Lam ◽  
Xingyu Wang ◽  
Daniel W. C. Ho
Keyword(s):  
Feedback Linearization ◽  
Closed Loop ◽  
Loop System ◽  
Closed Loop System ◽  
Singularity Problem ◽  
Neural Controller ◽  
The Neural Network ◽  
Approximation Errors ◽  
Nonlinear Uncertainties ◽  
Adaptive Neural Controller

In this paper, the adaptive H∞ control problem based on the neural network technique is studied for a class of strict-feedback nonlinear systems with mismatching nonlinear uncertainties that may not be linearly parametrized. By combining the backstepping technique with H∞ control design, an adaptive neural controller is synthesized to attenuate the effect of approximation errors and guarantee an H∞ tracking performance for the closed-loop system. In this work, the structural property of the system is utilized to synthesize the controller such that the singularity problem of the controller usually encountered in feedback linearization design is avoided. A numerical simulation illustrating the H∞ control performance of the closed-loop system is provided.

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