Matteo Palpacelli

Kinematics of the 3-CPU Parallel Manipulator Assembled for Motions of Pure Translation

The paper describes the architecture of a novel parallel kinematics machine that is characterized by motions of pure translation. It is shown that the Cartesian arrangement of the 3 limbs assures simple kinematic relations and an isotropic workspace, without any rotation or translation singularity. Such good features should allow the design of parallel robots that are characterized by simple controllers and good performances, as an alternative to current mechanical schemes.

Shape memory actuator with slider and slot layout and single fan cooling

This work proposes a new shape memory actuator based on a slider and slot mechanism. The particular layout can be associated to a simplified air cooling with a single fan and results in a solid and reliable structure. Dimensioning of parts is described and preliminary experimental results are presented.

A Comparison between Position-Based and Image-Based Dynamic Visual Servoings in the Control of a Translating Parallel Manipulator

Two different visual servoing controls have been developed to govern a translating parallel manipulator with an eye-in-hand configuration, That is, a position-based and an image-based controller. The robot must be able to reach and grasp a target randomly positioned in the workspace; the control must be adaptive to compensate motions of the target in the 3D space. The trajectory planning strategy ensures the continuity of the velocity vector for both PBVS and IBVS controls, whereas a replanning event is needed. A comparison between the two approaches is given in terms of accuracy, fastness, and stability in relation to the robot peculiar characteristics.

A lockable spherical joint for robotic applications

The paper proposes the mechanical design of a lockable spherical joint, which is designed to be manually or automatically configured in different kinematic solutions. In fact it can be used as a conventional spherical joint or converted in a universal joint or still downgraded to a revolute joint. Therefore different configurations can be chosen according to user needs. In particular, two of the three axes of revolution, arranged in the typical roll-pitch-roll sequence of robot spherical wrists, can be locked alternatively in order to provide two differently arranged U-joints. It can be demonstrated that such behavior allows to activate different mobilities of two classes of reconfigurable parallel kinematics manipulators. The transition between such mobilities occurs exploiting the concept of over-constrained kinematics, which is realized by the lockable joint during the switching phase in order to avoid an instantaneous mobility of the robot.

Mobility Analysis of Non-overconstrained Reconfigurable Parallel Manipulators with 3-CPU/3-CRU Kinematics

The paper presents two reconfigurable non-overconstrained parallel kinematics machines, whose moving platform can translate or rotate according to the configuration of a specific joint. They share similar leg kinematics: both manipulators have a cylindrical joint and a universal joint, which are used to connect each leg respectively with the fixed base and the moving platform. On the contrary, the manipulators differ for the intermediate joint between the two members that make up each leg: a prismatic and a revolute joint. The universal joint can be actually thought of as a spherical lockable joint, featured by a serial kinematics of three revolute axes. Two of them can be locked alternately in order to provide two different universal joint configurations, which confer the two mentioned mobilities on both manipulators. Screw theory is used to geometrically demonstrate their mobility.

Experimental identification of the static model of the HPKM Tricept industrial robot

The present paper addresses the modelling and the experimental identification of the static behaviour of the Tricept robot, a hybrid parallel kinematic machine. Mass properties of robot links are initially hypothesized from solid modelling and then incorporated in the identification procedure. Coulomb friction and gravity contributions to motor torques are taken into account: their identification is carried out by means of ordinary least-squares algorithms based on motor currents measurements during several slow motion tests. Moreover, the effect of external forces applied at the end-effector is introduced in the model and analysed by driving the robot end-effector against a calibrated compliant cell. Eventually, the static model is profitably used in an industrial operation of Friction Stir Welding to estimate the external forces applied at the tool mechanical interface providing some benefits: a deeper understanding of the technological process parameters and the possibility to realize model-based controls. Graphical Abstract

Sensitivity analysis of a mini pointing device

The paper presents a preliminary study needed to carry out a kinematic calibration procedure for a mini pointing device. The latter inherits its kinematics from a conventional five-bar linkage. A sensitivity analysis of all the geometric parameters involved in the kinematic model of the device is performed within the device workspace. A model is proposed by assuming a non overconstrained kinematics for the machine. Such assumption allows to consider a coupled rotational and translational motion of its moving platform, that is usually designed to have a fixed center of rotation. Results show how the model can be simplified without a significant reduction of its position accuracy, at least in a significant region of the manipulator workspace.

Kinematic analysis and synthesis of a novel gripper for dexterous applications

This paper demonstrates kinematic analysis and synthesis of a novel, modular, reconfigurable gripper, which is capable to manipulate plurality of object. The gripper consists of four identical modular fingers, dexterous among all axes. Each modular finger of the gripper is conceived to the aim of satisfying efficient grasping, manipulation and also object release with accordance of desired posture. The proposed gripper has 16 DOFs, which can be reduced by decreasing the number of fingers depending on its target uses. In this paper, the in-hand manipulation capability is explained from kinematic perspective and some analysis carried through to synthesize the gripper for user specific applications.

Robotic Friction Stir Welding of AA5754 Aluminum Alloy Sheets at Different Initial Temper States

Robotic friction stir welding experiments were performed on AA5754 aluminium alloy sheets, 2.5 mm in thickness, in two different temper states (H111 and O-annealed). A six axes robot with a hybrid structure, characterised by an arm with parallel kinematics and a roll-pitch-roll wrist with serial kinematics, was used. The effect of the process parameters on the macro-and micro-mechanical properties and microstructure of joints was widely analysed. It was shown that, under the same process condition, the mechanical properties of the joints are strongly influenced by the initial temper state of the alloy. In particular, as AA5754-H111 is welded, the ultimate tensile strength is not significantly affected by the process parameters whilst the ultimate elongation significantly depends on the welding speed. In AA5754-O, both ultimate values of tensile strength and elongation are affected by the welding speed whilst a negligible effect of the rotational speed can be observed. Irrespective of the welding parameters, the H111 temper state leads to mechanical properties higher than those given by the O-annealed state. An investigation has been also carried out in order to evaluate the micro-hardness profiles and microstructure of the FSWed joints in order to understand the mechanisms operating during robotic friction stir welding.

Multibody Analysis and Design of a Reconfigurable Parallel Kinematics Manipulator

This paper presents the design of a reconfigurable parallel kinematics machine endowed with three degrees of freedom of pure translation, or alternately of pure rotation. Such reconfigurability results from the use of lockable spherical joints, which realize the connection between each robot leg and the moving platform. Three actuated legs are used to drive the platform motion. The change of configuration occurs only at a specific pose, called home configuration. A control strategy allows to manage the shift phase and activate the two mobilities one at a time. Multibody simulations allowed to analyze the dynamic behavior of the manipulator and to verify the choices made with regard to the robot mechanics and the size of actuation systems. Position and differential kinematics of the manipulator are briefly introduced in order to demonstrate the simplicity of the analytic expressions and the mechanical feasibility of the manipulator.Copyright