Ch. Pinto

A symmetric parallel schönflies-motion manipulator for pick-and-place operations

This paper presents a new symmetric parallel Schonflies-motion generator. The design is an evolution of a previous robot with linear inputs. The complete kinematic analysis of the 4-degree-of-freedom (dof) parallel manipulator is presented. The degrees of freedom are obtained from the Group Theory, the direct and inverse position problems are solved obtaining the manipulators workspace, and the Jacobian analysis is presented. Then the isotropic configurations of the manipulator are discussed and the local dexterity map within the workspace is produced. Finally, two alternatives of a rotational mechanical device, which will increase the angular end-effector range, are proposed.

Analysis of the components of discretization error in non-linear structural problems

The present paper considers the reliability of finite-element analysis where non-linear planar structural problems (large strains and plasticity) are concerned. Error estimators of the flux-projection type, based on strain power density, are used. A study of the various components of error discretization is made as a function of parameters such as load step or the number of degrees of freedom of the finite-element model. Two numerical examples are selected so that certain properties of these estimators are demonstrated. Conclusions of practical use can be drawn from the results expressed in tables and charts.

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.

A Robot for Welding Inspection in Offshore Mooring Chains

In this paper, the authors present the CIRUS robot. This automatic system uses a combination of pulse-echo and pitch and catch ultrasonic strategies for the inspection of the welded area of mooring chain links in an automatic way. The robot is divided in three parts: global positioning subsystem, local positioning subsystem and inspection subsystem. Additionally, a data acquisition subsystem processes the results of the verification and produces a report for the inspector allowing the traceability of the product for assuring the welding quality.

A robot for non-destructive testing weld inspection of offshore mooring chains

Welding flaw detection is a key step in manufacturing many components. In offshore chains, every link is manufactured from a steel bar that is bent and the ends joined by flash butt welding. Ultrasonic inspection of the welded area is required for classification. Defects, if any, are parallel to the welded area, which do not favour detection by manual inspection with 45° beams, as per usual practice . This article reports on CIRUS, a robot developed for automatic inspection of the weld area using a combination of pulse-echo and pitch-catch ultrasonic testing. The robot kinematic structure includes global positioning, local positioning and inspection subsystems, and each subsystem design is described in detail. A data acquisition system processes ultrasonic inspection results and provides visual information for the inspector as well as traceability for quality manufacturing.

Experimental Validation of the Mechatronic Model of a Parallel Manipulator

In this paper, a mechatronic model of a planar parallel manipulator is developed and experimentally validated. The model considers the dynamics of the actuators, as well as the PID control algorithm with position, velocity and current cascaded loops and their timing. As our main contributions, the dynamics of the manipulator have been solved using the principle of equivalent energy to split up the closed-loop mechanism, and the torque calculated is regarded as a disturbance on the actuators, avoiding solving the forward dynamic problem. Also, the dynamics of the actuators take into account the inertia and the friction parameters, which have been experimentally identified by means of a grey-box identification method. Several experiments have been carried out on a prototype, varying the motion profile, the velocity and acceleration, and the position control gain. The results show a reasonable correlation and provide the basis for further discussion.

Restoration and Digital Display of Max Kohl Mechanisms in the Engineering School of USAL

Max Kohl Company, in Chemnitz (Germany), was a manufacturer of educational mechanisms that were distributed all around the world. In the early twentieth century, the University of Salamanca (USAL) bought some of them for the Engineering School of Bejar. Now, this collection of mechanisms is being restored by a group of professors of the Engineering School. The mechanism characterization was carried out with the help of Max Kohl Chemnitz catalogues. This initiative and other are being discovered by researchers working in the European Project thinkMOTION. The thinkMOTION Project aims to create the world’s largest open-access digital library of content in the field of machines and mechanisms. This paper shows brief descriptions of some the mechanisms and the way they look like once they are uploaded to the digital library.

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.

Real-Time Validation and Control Environment for Parallel Robot Control Design

Due to their high performance when executing high-speed and accurate tasks, parallel robots have became the focus of many researchers and companies. However, exploiting the full potential of these robots requires a correct mechatronic design, in which the designed mechanism has to be controlled by a suitable control law in order to achieve the maximum performance. In this paper a novel Validation and Control Environment (VALIDBOT) is proposed as a support for the control design and experimental testing stages of these robots. The proposed open and flexible environment is designed to meet rapid prototyping requirements, offering a high level framework for both students and researchers. The capabilities of the environment are illustrated with an application case based on a 5R parallel robot prototype in which a modified CTC controller is tested.Copyright

Structural Dynamic Analysis of Low-Mobility Parallel Manipulators

This paper focuses on the study of static and dynamic stiffness (normal modes and natural frequencies) by a method which enables to evaluate the vibration behaviour of low mobility parallel manipulators, i.e., less than 6 degrees-of-freedom. The purpose of this study is to improve the structural behaviour of this type of manipulators under the effect of static and dynamic external loads. As a starting point, we use a previously developed methodology for static rigidity obtaining for the aforementioned manipulators characteristics, using as case study DAEDALUS I parallel robot. The method is applied to a simplified model to analyze the evolution of the static stiffness, the frequencies and normal modes in the whole workspace. The method involves the use of one analytical model, other numerical, based on finite elements and a comparison with an experimental campaign on a prototype. From this study, the results of the natural frequencies trends of the manipulator are represented in tridimensional maps.