Conventional Parallel Manipulators Research Articles

Design and analysis of novel kinematically redundant reconfigurable generalized parallel manipulators

A conventional parallel manipulator (PM) generally employs independent serial kinematic chains to support one rigid moving platform. Compared with PMs, generalized parallel manipulators (GPMs) with configurable platforms can improve the kinematic performance and functionality. This paper highlights the idea of designing and analyzing novel GPMs with configurable platforms. Firstly, the type synthesis of GPMs is performed. Then a novel class of reconfigurable GPMs with remotely operated grippers is constructed. Secondly, the motion-screw system and the reconfiguration property of the manipulator are analyzed based on screw theory. Moreover, the position analysis of the GPM is carried out to evaluate the workspace and reveal the motion characteristics. Furthermore, the numerical examples and simulation results are obtained to demonstrate the presented methodology. The feasible arrangement of the actuated joints is studied and the potential application of the GPM is discussed. Finally, a prototype is manufactured to illustrate the advocated design philosophy and the functionality of the GPM.

A new family of generalized parallel manipulators with configurable moving platforms

A Conventional Parallel Manipulator (CPM) usually uses a rigid moving platform as the end-effector to connect serial legs. Since serial legs independently support the platform, kinematic joints are embedded into the rigid moving platform. However, the moving platforms of Generalized Parallel Manipulators (GPMs) are not limited to rigid bodies. The introduction of configurable platforms with integrated end-effectors allows for providing a multipoint connection with the environment. As a result, the functionality of parallel manipulators can be further extended. Resulting from the property of the platform, a significant challenge of connecting moving platforms with serial limbs is posed. This paper puts forward a systematic method for synthesizing parallel manipulators with configurable platforms. To realize the cooperation of the integrated end-effectors, the multi-drive hybrid limbs are designed base on the screw theory. According to the constraint synthesis method, a novel class of parallel manipulators with configurable platforms is constructed. Then the examples with different motion patterns are offered to corroborate the effectiveness of the proposed method. At last, driving schemes and the potential applications of the derived manipulators are discussed.

A novel class of generalized parallel manipulators with high rotational capability

A conventional parallel manipulator is characterized by connecting one moving platform with two or more serial kinematic limbs. Since each limb is independently supporting one moving platform, the moving platform must be a rigid body with several kinematic pairs fixed on it. However, for generalized parallel manipulators with articulated moving platforms, the moving platforms are not limited to rigid bodies but including serial kinematic chains or internal kinematic joints. The introduction of articulated moving platforms allows for improving the kinematic performance of generalized parallel manipulators, especially for rotational capability. On account of the structural characteristics of the moving platforms, it also poses a significant challenge in the construction of the structures of manipulators. This research raises a new method for the type synthesis of generalized parallel manipulators with novel articulated moving platforms. The proposed method introduces a striking shortcut for the limb structure analysis of mechanisms with high rotational capability. In this paper, a class of generalized parallel manipulator with different degrees of freedom from 3 to 6 are constructed by using the constraint synthesis method, and several examples are provided to demonstrate the feasibility of the advocated method. At last, the 3T3R generalized parallel manipulator is taken as an example to analyze the inverse kinematics, and the evaluation of the workspace is conducted to verify the rotational capacity.

Oscillation Reduction and Frequency Analysis of Under-Constrained Cable-Driven Parallel Robot with Three Cables

SummaryCable-driven parallel robots (CDPRs) possess a lot of advantages over conventional parallel manipulators and link-based robot manipulators in terms of acceleration due to their low inertia. This paper deals with under-constrained CDPRs, which manipulate the end-effector to carrying the payload by using a number of cables less than six, often used preferably owing to their simple structures. Since a smaller number of cables than six are used, the end-effector of CDPR has uncontrollable degrees of freedom and that causes swaying motion and oscillations. In this paper, a scheme to curb on the unwanted oscillation of the end-effector of the CDPR with three cables is proposed based on multimode input shaping. The precise dynamic model of the under-constrained CDPR is obtained to find natural frequencies, which depends on the position of the end-effector. The advantage of the proposed method is that it is practicable to generate the trajectories for vibration suppression based on multi-mode input-shaping scheme in spite of the complexity in the dynamics and the difficulty in computing the natural frequencies of the CDPR, which are required in any input-shaping scheme. To prove the effectiveness of the proposed method, computer simulations and experiments were carried out by using 3-D motion for CDPR with three cables.

Design and analysis of a partially decoupled generalized parallel mechanism for 3T1R motion

Compared with conventional parallel manipulators with serial kinematic chains supporting a nonflexible platform, generalized parallel mechanisms may be further constrained by interconnected coupling sub-chains or configurable platforms. The additional coupling sub-chains and configurable platforms have the potential advantages of improving overall characteristics and executing specific output motions. Based on the applications, this paper proposes a symmetric generalized parallel mechanism with so-called Schönflies motion. This mechanism can generate three independent translations in conjunction with a partially decoupled rotation which refers to a given direction. To improve the dynamic performance, all the actuators are installed on the fixed platform. The paper starts with the number synthesis of independent loops that can derive all possible non-isomorphic contracted graphs of the 3T1R generalized parallel mechanism. The threefold-symmetric Bricard linkage is introduced into the generalized parallel mechanism. Besides, several novel generalized parallel mechanisms with various motion patterns are provided. The kinematic analysis of the proposed architecture is established. The evaluation of the workspace is conducted. Finally, the study of the overall Jacobian matrix is performed and the singularity including kinematic singularity and constraint singularity is analyzed.

A 7-DOF redundantly actuated parallel haptic device combining 6-DOF manipulation and 1-DOF grasping

Parallel manipulators are often used in haptic applications since they usually offer higher stiffness and lower inertia than their serial counterparts. However, classical parallel haptic devices generally do not provide grasping capabilities since all their motors are located at the base. This article presents a new 7-DOF robotic architecture, which has the particularity of providing 1-DOF grasping in addition to 6-DOF manipulation while all actuators are located at the base. This is possible thanks to the use of a novel configurable platform that replaces the single rigid body normally used as end-effector in conventional parallel manipulators. The grasping capability of this haptic device is part of the mechanical architecture itself and can be fully controlled from base-located motors. In this article, the architecture, kinematic analysis, kinematic performance, design, and implementation of the novel 7-DOF parallel haptic device are described.

DYNAMIC MODELING OF LONG SPAN NEW MATERIAL CABLE ROBOT

Cable driven parallel manipulator (CDPM) is a robotic mechanism which utilize multiple actuated cables to manipulate objects. It offers some advantages over the conventional parallel manipulators, such as higher load to weight ratio and larger workspace. These advantages are more evident if one uses composite materials for the cables of CDPM. This study aims at dynamic analysis and trajectory path planning of long-span CDPM by taking into accounts the effects of mass, curvature, flexibility and viscoelastic behavior of its new material cables. The dynamic analysis of the CDPM shows that its end effector vibrates throughout its desired trajectory which leads to an oscillatory pose error. An optimization algorithm is used here for the error suppression of the path planning problem.

Structural synthesis of parallel manipulators with coupling sub-chains

A conventional parallel manipulator uses serial kinematic chains or the legs to support a single moving platform. The movement of the platform may be further constrained by adding interconnections among its legs to form the so-called coupling sub-chains. The introduction of coupling sub-chains to the kinematic structures of parallel manipulators, while allowing for improved performance and functionality, presents also significant challenges in the structural synthesis of the resulting manipulators. This paper presents a systematic method for the structural synthesis of parallel manipulators with coupling sub-chains. The contracted graphs in connection with Euler's equation are constructed based on permutation and combination, and the isomorphism is identified. Then, fractionation and simplification process of the contracted graph of the resulting manipulators are analyzed. In the second half of the paper, a screw theory based method for constraint synthesis of kinematic chains is developed to synthesize various legs and coupling sub-chains. Examples were provided to demonstrate the efficacy of the advocated method.

Kinematic analysis of a flexible six-DOF parallel mechanism

In this paper, a new type of six-degrees of freedom (DOF) flexible parallel mechanism (FPM) is presented. This type of parallel mechanism possesses several favorable properties: (1) its number of DOFs is independent of the number of serial chains which make up the mechanism; (2) it has no kinematical singularities; (3) it is designed to move on rails, and therefore its workspace is much larger than that of a conventional parallel manipulator; and (4) without changing the number of DOFs and the kinematics of the mechanisms, the number of the serial chains can be reconfigured according to the needs of the tasks. These properties make the mechanism very preferable in practice, especially for such tasks as joining huge ship blocks, in which the manipulated objects vary dramatically both in weights and dimensions. Furthermore, the mechanism can be used as either a fully actuated system or an underactuated system. In the fully actuated case, the mechanism has six DOF motion capabilities and manipulation capabilities. However, in the underactuated case, the mechanism still has six DOF motion capabilities, but it has only five DOF manipulation capabilities. In this paper, both the inverse and forward kinematics are studied and expressed in a closed form. The workspace and singularity analysis of the mechanism are also presented. An example is presented to illustrate how to calculate the kinematics of the mechanism in both fully-actuated and underactuated cases. Finally, an application of such a mechanism to manufacturing industry is introduced.