Giacomo Palmieri

Analysis and Design of a Reconfigurable 3-DoF Parallel Manipulator for Multimodal Tasks

This paper presents the design of a reconfigurable 3-DoF parallel kinematics manipulator. The main feature of the device is the ability to change the mobility of its moving platform from pure translation to pure rotation. The manipulator kinematics is conceived so that, when a particular configuration of the manipulator is reached, the transition between the two working modes is possible by changing the configuration of a metamorphic universal joint, which is used to connect the legs of the manipulator with the moving platform. The mechanical design of the joint, which is in fact a lockable spherical joint, is illustrated. With the joint integrated into the robot architecture, an instantaneous overconstrained kinematics is exploited to manage the phase of reconfiguration of the whole mechatronic device. A kineto-static analysis provides information about the influence of geometric parameters on its functional design. The manipulator shows simple kinematics and statics models, as well as good kinematic and static performances. Eventually, the versatility of the manipulator is shown by proposing some advanced manufacturing applications in which it could find use.

Analysis of kinematics and reconfigurability of a spherical parallel manipulator

This paper presents the kinematic characterization of a 3-Cylindrical-Prismatic-Universal (3-CPU) parallel manipulator designed for motions of pure rotation. The machine has been conceived at the Polytechnic University of Marche, and recent studies have shown that its kinematic architecture can be exploited for the realization of reconfigurable machines with different kinds of motions (pure rotational, pure translational, and planar motions among others). The 3-CPU concept has been subject to further investigations for a deeper understanding of this peculiar behavior. After a brief introduction to these concepts, the paper faces the position and the differential kinematics of the 3-CPU spherical manipulator aiming at identifying workspace boundaries and its kinematic manipulability.

Parallel Wrists for Enhancing Grasping Performance

Good grasping and effective manipulation heavily depend on the performance of robotic wrists such as, e.g., the number of degrees of freedom, the kind of motion that is generated, the dexterity of the operations, the stiffness, and the size of the mechanical structure; such characteristics heavily affect kinematic and dynamic performance of the manipulation and can lead to a successful grasp or to an unexpected failure, if not taken into consideration since the early design steps. This chapter, after an introduction recalling the wrist structure of the industrial manipulators, focuses on parallel kinematics wrists, a rather new kind of mechanical architecture that has not found so far relevant industrial applications but shows very promising features, such as mechanical stiffness, high accuracy, lightweight construction, and so on. After presenting a powerful kinematical tool for the synthesis of parallel kinematics machines (SPM), which is based on Lie algebra, the design of a novel spherical wrist is discussed in details. A prototype machine, actuated by three brushless linear motors, has been built with the aim of obtaining good static and dynamic performance.

Details on the Design of 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. The device is conceived for being used as a conventional spherical joint or converted in a universal joint, or still downgraded to a revolute pair. 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 alternately in order to provide two differently arranged universal joints. It can be demonstrated that such behavior allows to activate different mobilities of a class of reconfigurable parallel kinematics manipulators and for this task the device has been dimensioned. 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.

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.

Position Control of a 3-CPU Spherical Parallel Manipulator

The paper presents the first experimental results on the control of a prototypal robot designed for the orientation of parts or tools. The innovative machine is a spherical parallel manipulator actuated by 3 linear motors; several position control schemes have been tested and compared with the final aim of designing an interaction controller. The relative simplicity of machine kinematics allowed to test algorithms requiring the closed-loop evaluation of both inverse and direct kinematics; the compensation of gravitational terms has been experimented as well.

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.