Sharif Digital Repository

One of the most challenging problems in dealing with parallel manipulators is identifying their forward singular configurations. In such configurations these mechanisms become uncontrollable and cannot tolerate any external force. In this article a geometrical method, namely Constraint Plane Method (CPM), is introduced with the use of which one can easily obtain the singular configurations in many parallel manipulators. CPM is a methodical technique based on the famous Ceva plane geometry theorem. It is interesting to note that CPM involves no calculations and yields te result quickly. In addition, some of the previous geometrical methods led to many separate singular configurations;... 

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... 

New methods for the Inverse and forward kinematic analysis of the novel six Degrees of Freedom (6DOF) parallel manipulator which has only two legs are presented. The actuation of the new mechanism is through two base-mounted spherical actuators. In the inverse pose kinematic, active joint variables are directly calculated with no need for the evaluation of passive joint variables. In the forward pose kinematic, closed form solution adopting a new approach is presented. It is shown that the inverse and forward pose kinematic have sixteen and four different solutions, respectively. Moreover, closed form equations for the rate kinematic analysis are proposed. Finally, two different categories... 

In this article singular points of a parallel manipulator are obtained based on a novel geometrical method. Here we introduce the constrained plain method (CPM) and some of its application in parallel mechanism. Given the definition of constraint plane (CP) and infinite constraint plane (ICP) the dependency conditions of constraints is achieved with the use of a new theorem based on the Ceva geometrical theorem. The direction of angular velocity of a body is achieved by having three ICPs with the use of another theorem. Finally, with the use of the above two novel theorems singularities of the 3UPF_PU mechanism are obtained. It should be emphasized that this method is completely geometrical,... 

In this paper conception and dynamic modeling of a snake-like robot with passive wheels and compliant joints is investigated. The proposed robot has the ability to follow a socalled Serpenoid curve passively by using an appropriate set of initial conditions. Introduction of a unique structure at each joint enables the robot to achieve passive motion. A torsional spring is used in series with an actuator between each two consecutive links. Using wheels at the middle of each link imposes many non-holonomic constraints to the system. These constraints reduce the degrees of freedom of the system to only two. Due to the existence of these non-holonomic constraints, dynamic equations governing the... 

In this paper we present a novel planar structure of a snake-like robot. This structure enables passive locomotion in snake-like robots through an auxiliary link in joint and a torsional spring. Dynamic equations are derived, using Gibbs-Appell method. Kinematic model of the robot include numerous non-holonomic constraints, which can be omitted at the beginning by choosing proper coordinates to describe the model in Gibbs-Appell framework. In such a case, dynamic equations will be significantly simplified, resulting in significant reduction of simulation time. Simulation results show that, by proper selecting initial conditions, joint angles operate in a limit cycle and robot can locomote... 

The insect circulatory system contains an open hemocoel, in which the mechanism of hemolymph flow control is ambiguous. As a continuous fluidic structure, this cavity should exhibit pressure changes that propagate quickly. Narrow-waisted insects create sustained pressure differences across segments, but their constricted waist provides an evident mechanism for compartmentalization. Insects with no obvious constrictions between segments may be capable of functionally compartmentalizing the body, which could explain complex hemolymph flows. Here, we test the hypothesis of functional compartmentalization by measuring pressures in a beetle and recording abdominal movements. We found that the...