Javier Corral

A methodology for static stiffness mapping in lower mobility parallel manipulators with decoupled motions

In this paper a general methodology for obtaining static stiffness maps in lower mobility parallel manipulators is proposed. The main objective is to define a set of guidelines, which allow the experimental work to be optimized and computational time to be reduced. First, a two-degree-of-freedom (DOF) mechanism will be used for methodology validation, since it is the stiffness of the basic kinematic chain of the manipulator that is to be analysed. Two mathematical models of this mechanism and an experimental prototype will be considered for the validation. After that, the methodology will be applied to a lower mobility (4-DOF) parallel manipulator. In this paper, the experimental prototype and its set-up is highly important because some particular features of the experimental analysis will be defined. This paper introduces a key experimental tool: the preload, which allows the clearances and possible assembling errors to be considered. The added value from the application of this procedure is the obtaining of graphs that describe, in an intuitive and useful way, the behaviour of the manipulators stiffness inside its workspace as a function of the mobile platform position and orientation.

Kinematic Analysis of a Flexible Tensegrity Robot

In the field of parallel kinematics few designs use highly deformable elements to obtain the end effector movement. Most compliant mechanisms rely on notches or shape changes to simulate a standard kinematic joint. In this work a kinematic model of a simple parallel continuum mechanism that combines a deformable element and cable is presented. The kinematic model is used to study the workspace of the manipulator and is validated by experimental measurements of a prototype.

Robust Model Based Predictive Control for Trajectory Tracking of Parallel Robots

Model Based Predictive Control (MPC) is an interesting approach due to its ability to consider the constraints of the controlled system and easily adapt to the future reference changes. In this paper, a novel robust MPC controller is presented, which considers the effect of the Tool Center Point (TCP) estimation errors and the model uncertainties of the mechanical structure. In order to show its effectiveness, its application to the 5R parallel manipulator is detailed. Simulation validation is provided to demonstrate that the proposed approach can exploit all the theoretical capabilities of the mechatronic system.

Dynamic Capabilities of a Parallel Robot Based Routing Machine

In this paper, a study of the capabilities of a parallel manipulator with four degrees of freedom for machining application is presented. Specifically, routing tasks will be considered. To carry out this study, a process model that allows the dynamic behaviour of robot based on the phenomenon of chatter to be considered is used. The model takes into account characteristics of the process like the tool, the material to be machined and spindle speed. The dynamic stiffness of the manipulator is also taken into account. This modal parameter has a decisive influence on the dynamic behaviour. Using a single-frequency model of stability, values of the critical depth of cut and chatter frequency are obtained. Since the structural behaviour of parallel manipulators is a function of the location in the workspace, a post-processing of both critical depth of and chatter frequency is presented. From these maps, the dependence of the depth of cut and chatter frequency on the location is also derived.

Kinematic Analysis of a Continuum Parallel Robot

Continuum Parallel Robots are mechanical devices with closed loops where kinematic pairs have been eliminated and motion is obtained by large deformations of certain elements. Most compliant mechanisms use notches in thick elements to produce the effect of kinematic pairs. A few are designed so that slender elements can deform and produce the desired motion. Some microelectromechanical systems have used this principle to create bistable planar mechanisms. The purpose of this work is to extend such principle in the field of macro mechanisms for manipulation. The aim is to design the counterparts to some classical parallel manipulators solving the corresponding kinematic problems. In doing this, the authors will have to work out the most efficient way to solve a position problem where geometry and forces are involved. Such compliant mechanisms could be combined in the future with tensegrity systems to enhance the available workspace. In this first report we will focus on the simplest planar parallel mechanism of two degrees of freedom.

Using the ThinkMOTION Project Resources for the Teaching of Mechanism and Machine Theory

The thinkMOTION project, as a part of Europeana (www.europeana.eu) leads to the world’s largest free access digital library in the field of motion systems, which is very useful for all technical subjects and in particular for Mechanism and Machine Theory. The project helps to make a significant improvement in the quantity and quality of these digital contents establishing a new kind of digital library in Europeana with focus on technical knowledge. The collected material is processed and presented immediately in a multilingual interactive portal via Europeana. Hence, the techno-cultural heritage and the current developments in motion science are preserved and made accessible for a wide range of European user groups as scientists, lecturers or students. The provided interactive material leads to a deeper understanding and motivates the students to learn more about the motion systems and machine design approaches. All kinds of material are considered (e.g. books, journals, drawings, images, physical models) to establish a digital library that connects historical and recent content from different countries. Six content providers spread over Europe are part of the project consortium. The open access to high quality material of historical and recent content from different countries opens new possibilities in multilingual searching, browsing and using of information sources.

Simplified Kinetostatic Model of the 3-PRS Manipulator

A comparative study of the dynamics of the 3-PRS parallel mechanism between the full case, considering the parasitic motions, and a simplified one, ignoring the parasitic motions, is presented in this work. A simplified dynamic model would be of great interest to determine the dimensions of the actuators and to solve the dynamic problem much easier and faster. The dynamic problem of the manipulator is studied using the Newton-Euler approach and a simulation in Matlab verifies that the parasitic motions can be ignored in the dynamic problem, for some given conditions.

Actuators Orientation Influence in the Energy Consumption of the 3-PRS Manipulator

In this work, a comparative study of the energy needed to run a 3-degree of freedom (DOF) parallel manipulator (PKM) for two different configurations of the inputs and two different transformation matrices for a concrete trajectory is presented. The 3-PRS is a PKM of low mobility, i.e., it has less than 6-DOF and when the main motion takes place, unexpected motions in the constrained DOF appear. These are parasitic motions. As previous studies show, these parasitic motions lead to less accuracy and, therefore, they are not desired from the point of view of the kinematics. It would be of great interest to know if the parasitic motions affect the dynamics as well and, if so, in which way. Thus, with those parasitic motions in mind, the inverse kinematic problem of position, velocity and acceleration is solved. Once the accelerations of all the elements have been derived, the rigid solid dynamics and the results of force requirements and power consumption in inputs are analysed. The trajectory studied is a rotation about an axis in a plane Pu,v in a mobile reference frame and the parasitic expressions depend on the transformation matrix combination used. In this paper, the results for two of those transformation combinations are presented for two configurations of the inputs — in the first one, the inputs are in a horizontal plane, while in the second one they are vertical.Copyright