Relevance and Transferability for Parallel Mechanisms With Reconfigurable Platforms

2019 ◽  
Vol 11 (3) ◽  
Author(s):  
Xi Kang ◽  
Jian S. Dai
Keyword(s):  
System Theory ◽  
Parallel Mechanism ◽  
Geometric Model ◽  
Parallel Mechanisms ◽  
End Effector ◽  
Kinematic Coupling ◽  
Reconfigurable Platforms ◽  
Reconfigurable Platform

The parallel mechanism with a reconfigurable platform retains all advantages of parallel mechanisms and provides additional functions by virtue of the reconfigurable platform, leading to kinematic coupling between limbs that restricts development of the mechanism. This paper aims at dealing with kinematic coupling between limbs by investigating the transferability of limb constraints and their degrees of relevance to the platform constraints based on the geometric model of the mechanism. The paper applies screw-system theory to verifying the degree of relevance between limb constraint wrenches and platform constraint wrenches, and reveals the transferability of limb constraints, to obtain the final resultant wrenches and twists of the end effector. The proposed method is extended to parallel mechanisms with planar n-bar reconfigurable platforms, spherical n-bar reconfigurable platforms, and other spatial reconfigurable platforms and lends itself to a way of studying a parallel mechanism with a reconfigurable platform.

scholarly journals Repeatability Analysis of Overconstrained Kinematic Coupling Using a Parallel-Mechanism-Equivalent Model

2020 ◽  
Author(s):  
Jianzhong Ding ◽  
Xueao Liu ◽  
chunjie wang
Keyword(s):  
Parallel Mechanism ◽  
Sampling Method ◽  
Contact Forces ◽  
Equivalent Model ◽  
Parallel Mechanisms ◽  
Kinematic Coupling ◽  
Contact Points ◽  
Prismatic Joints ◽  
Type Coupling ◽  
Additional Support

Abstract A novel method for repeatability analysis of overconstrained kinematic coupling using a parallel-mechanism-equivalent-model is proposed. An overconstrained Kelvin-type coupling with one additional support is introduced and used for method illustration. Contact forces of the overconstrained coupling under preload are computed with Moore-Penrose inverse and the deformations are obtained using the Hertz theory. The couping is equivalently modeled as a 7-SPS parallel mechanism, spherical joints of which represent the centers of the supporting balls and the contact points, respectively, and prismatic joints are used to simulate the deformations. Therefore, pose error of the coupling arisen from preload is analyzed using the well-appraised incremental method for forward kinematics analysis of parallel mechanisms. The uncertainties of the preload are discussed and a boundary-sampling method is proposed for repeatability analysis. The main contribution of this study lies in that the proposed parallel-mechanism-equivalent-model and the boundary-sampling method greatly simplify the repeatability analysis of overconstrained kinematic couplings. Finally, the proposed methods are validated by case study.

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.

A Quasi-Static Model for Planar Compliant Parallel Mechanisms

2009 ◽  
Vol 1 (2) ◽  
Author(s):  
Cyril Quennouelle ◽  
Clément Gosselin
Keyword(s):  
Parallel Mechanism ◽  
Applied Load ◽  
Jacobian Matrix ◽  
Static Model ◽  
Parallel Mechanisms ◽  
Compliance Matrix ◽  
End Effector ◽  
Kinematic Constraints ◽  
Compliant Parallel Mechanism ◽  
External Loads

In this paper, the mobility, the kinematic constraints, the pose of the end-effector, and the static constraints that lead to the kinematostatic model of a compliant parallel mechanism are introduced. A formulation is then provided for its instantaneous variation—the quasi-static model. This new model allows the calculation of the variation in the pose as a linear function of the motion of the actuators and the variation in the external loads through two new matrices: the compliant Jacobian matrix and the Cartesian compliance matrix that give a simple and meaningful formulation of the model of the mechanism. Finally, a simple application to a planar four-bar mechanism is presented to illustrate the use of this model and the new possibilities that it opens, notably the study of the kinematics for any range of applied load.

scholarly journals Collision-free workspace of parallel mechanisms based on an interval analysis approach

Robotica ◽  
2016 ◽  
Vol 35 (8) ◽  
pp. 1747-1760 ◽  
Author(s):  
MohammadHadi FarzanehKaloorazi ◽  
Mehdi Tale Masouleh ◽  
Stéphane Caro
Keyword(s):  
Interval Analysis ◽  
Parallel Mechanism ◽  
Spherical Shape ◽  
Stewart Platform ◽  
Analysis Approach ◽  
Parallel Mechanisms ◽  
Planar Case ◽  
End Effector ◽  
Mechanical Interference

SUMMARYThis paper proposes an interval-based approach in order to obtain the obstacle-free workspace of parallel mechanisms containing one prismatic actuated joint per limb, which connects the base to the end-effector. This approach is represented through two cases studies, namely a 3-RPR planar parallel mechanism and the so-called 6-DOF Gough–Stewart platform. Three main features of the obstacle-free workspace are taken into account: mechanical stroke of actuators, collision between limbs and obstacles and limb interference. In this paper, a circle(planar case)/spherical(spatial case) shaped obstacle is considered and its mechanical interference with limbs and edges of the end-effector is analyzed. It should be noted that considering a circle/spherical shape would not degrade the generality of the problem, since any kind of obstacle could be replaced by its circumscribed circle/sphere. Two illustrative examples are given to highlight the contributions of the paper.

The Manta and the Kanuk: Novel 4-DOF Parallel Mechanisms for Industrial Handling

1999 ◽  
Author(s):  
Luc H. Rolland
Keyword(s):  
Parallel Mechanism ◽  
Kinematic Chain ◽  
Parallel Robot ◽  
Chain Structure ◽  
Parallel Robots ◽  
Parallel Mechanisms ◽  
End Effector ◽  
Low Mass ◽  
Loading And Unloading ◽  
Very High

Abstract Two novel 4-DOF very fast parallel robots were designed. This paper introduces the new parallel mechanism designs which are named the Manta and the Kanuk. In order to reduce manipulator overall costs, the actuator and encoder numbers are minimized to the exact effective degrees-of-freedoms (DOF) which is usually not the case in most parallel robot designs. The robots allow end-effector displacements along the three Cartesian translations and one platform transversal rotation. The two remaining rotations are blocked by the intrinsic mechanical structure including the rotation along the platform normal which is always limited in range. The main advantages are high stiffness through the multiple kinematic chain structure which allow for low mass designs. Moreover, they feature simple mechanical construction. Thus, it shall be possible to achieve very high throughput since high accelerations are feasible. To circumvent the known workspace limitations, the actuators were selected to be prismatic along linear axes. The applications are automated warehouse manipulation, mediatheque manipulation, machine tool tool changers, loading and unloading.

Optimal trajectory planning considering optimal torque distribution of redundantly actuated parallel mechanism

2018 ◽  
Vol 232 (23) ◽  
pp. 4410-4419 ◽  
Author(s):  
Sumin Park ◽  
Jongwon Kim ◽  
Giuk Lee
Keyword(s):  
Parallel Mechanism ◽  
Optimization Procedure ◽  
Optimal Operation ◽  
Operation Planning ◽  
Parallel Mechanisms ◽  
Planning Stage ◽  
End Effector ◽  
Torque Distribution ◽  
Redundantly Actuated ◽  
Two Stages

Previous studies on the optimal operation planning of redundantly actuated parallel mechanisms have focused on optimal torque distribution for a predefined trajectory. However, the optimized result obtained for a predefined trajectory cannot guarantee an optimal operation plan, because the torque distribution ability of a redundantly actuated parallel mechanism is highly dependent on the shape of the end-effector trajectory. Therefore, we can expect the redundantly actuated parallel mechanism performance to be enhanced when both the trajectory and torque distribution are optimized during the optimal operation planning stage. We propose a novel redundantly actuated parallel mechanism optimization procedure that can optimize both the end-effector trajectory and torque distribution. The proposed procedure is composed of two stages of optimizers, i.e. upper- and lower-level optimizers that generate the end-effector trajectory and distribute the torques along the generated trajectory, respectively. Composition of these two stages of the optimization procedure allows optimization of both the trajectory and torque distribution, despite the correlation between them. The proposed optimization procedure is simulated using two types of cost functions. All the simulation results show that the proposed procedure facilitates optimization of the end-effector trajectory and the torque distribution concurrently. Also, the cost function value is minimized to a greater extent than in the result with the optimal torque distribution along the initial trajectory.

Active Compliant Parallel Mechanisms

2014 ◽  
Author(s):  
Matthew Holgate ◽  
Thomas G. Sugar
Keyword(s):  
Parallel Mechanism ◽  
Gear Ratio ◽  
Parallel Mechanisms ◽  
Output Link ◽  
End Effector ◽  
Attachment Point ◽  
The Third ◽  
Output Torque ◽  
Compliant Parallel Mechanism ◽  
Parallel Fashion

In a novel compliant parallel mechanism, a motor and spring are arranged in a parallel fashion and are connected to a movable lever arm. The motor pushes and pulls on one attachment point and the spring stores and releases energy at a second attachment point. In a non-obvious choice, we do not attach the output link to the commonly thought of end-effector, but to the third link in the planar, parallel mechanism. The new mechanism allows the transmission ratio of the motor to be a function of the output angle and the force applied at the spring. For example, if there are no loads on the spring, the overall gear ratio is lowered, and the output speed can be increased. Conversely, if there are loads on the spring, the overall gear ratio is increased, and the output torque can be increased.

Optimal dimensioning of redundantly actuated mechanism for maximizing energy efficiency and workspace via Taguchi method

2016 ◽  
Vol 231 (2) ◽  
pp. 326-340 ◽  
Author(s):  
Sumin Park ◽  
Jehyeok Kim ◽  
Jay I Jeong ◽  
Jongwon Kim ◽  
Giuk Lee
Keyword(s):  
Energy Efficiency ◽  
Taguchi Method ◽  
Performance Index ◽  
Parallel Mechanism ◽  
Response Analysis ◽  
Parallel Mechanisms ◽  
End Effector ◽  
Controllable Factors ◽  
Redundantly Actuated ◽  
A Chain

A kinematic optimization of a redundantly actuated parallel mechanism is developed via the Taguchi method to maximize the sum of energy efficiency and workspace. In the optimization process, the energy consumption in a representative pathway of a predefined workspace is used as the performance index of the energy efficiency. The horizontal reach and stroke, and the vertical reach of mechanism, are used for the performance index of the workspace. The kinematic parameters of a chain that was added to the proposed non-redundantly actuated parallel mechanism as an extension to achieve redundant actuation are selected as the controllable factors. The velocity of the end-effector is considered to be a noise factor. Because the Taguchi method was originally used for robust optimization, we can improve the energy efficiency and workspace under various velocities for the end-effector. In the first stage of optimization, the number of controllable factors is reduced, and their correlations are eliminated using a response analysis. Quasi-optimized results are derived after the second stage of optimization. The optimized redundantly actuated parallel mechanism result is validated by comparing the energy efficiencies and workspaces of the original and optimal redundantly actuated parallel mechanisms.

scholarly journals A Dexterity Comparison for 6 DOF Hybrid Robots

2020 ◽  
Author(s):  
MohammadAli Mohammadkhani ◽  
Ahmad Reza Haghighi
Keyword(s):  
Parallel Mechanism ◽  
Parallel Manipulator ◽  
Parallel Manipulators ◽  
Parallel Mechanisms ◽  
End Effector ◽  
Hybrid Mechanisms ◽  
Six Dof ◽  
Position And Orientation

Abstract In this paper, new hybrid robots are suggested which divided the task into a position and orientation tasks. The position mechanism controls the position whereas the orientation one manipulates the orientation of the end effector. These robots consist of a translational parallel manipulator and a rotational serial or parallel mechanism. The 3UPU or Tricept parallel manipulator and a three-axis gimbaled system or parallel shoulder manipulator are chosen for translational and rotational movements, respectively. The main goal of this paper is analyzing the development and combination of serial and parallel manipulators in order to increase their features. According to this purpose, serial and parallel mechanisms with three DOF are combined in a way to encompass six DOF space. It is shown hybrid mechanisms with less coupling between their subsystems are capable of increasing robot characteristics.

Design and Kinematic Analysis of a Flexible-Link Parallel Mechanism With a Spatially Quasi-Translational End Effector

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Hao Pan ◽  
Genliang Chen ◽  
Yezheng Kang ◽  
Hao Wang
Keyword(s):  
Parallel Mechanism ◽  
Degrees Of Freedom ◽  
Accuracy Evaluation ◽  
Elastic Rods ◽  
Parallel Mechanisms ◽  
Flexible Link ◽  
Large Space ◽  
Compliance Matrix ◽  
End Effector ◽  
Principal Axes

Abstract Intrinsic passive compliance of flexible-link parallel mechanisms makes them suitable for situations where compliant manipulation is necessary. In this work, through using elastic rods as limbs, a flexible-link parallel mechanism whose end effector can move translationally with a large workspace is proposed. The middle plate and end effector are connected to the base via two groups of three elastic rods, which are arranged in a cylindrically symmetric way with a phase difference of 60 deg. Concurrently, the middle plate is coupled with the elastic rods connected to the end effector via sliding connection. Besides, a rotating set of coplanar wheels is introduced to provide smooth coupling for the prototype. Three actuation modules are used to drive the end effector, while another three to compensate toward its configuration deviations caused by deformation compatibility. Then, based on principal axes decomposition of compliance matrix, kinetostatics models for inverse and forward kinematics are established. The numerical analysis reveals that the end effector can make quasi 3-degrees-of-freedom (DOF) translation in a large space with extremely small twist. Finally, workspace experiments at four typical slices and pose accuracy evaluation along continuous trajectories are carried out, and the results demonstrate that our design and theoretical model are correct.

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