Luca Carbonari

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.

The Kinematotropic 3-CPU Parallel Robot: Analysis of Mobility and Reconfigurability Aspects

This paper investigates the mobility analysis of a 3-CPU parallel machine, aiming at checking the possibility to perform both pure rotational and pure translational motions. Machine kinematics is formalized by taking advantage of algebraic geometry principles that allow extracting the necessary constraint equations in form of polynomial ideals. The analysis of the sub-ideals deriving from the decomposition of the starting constraint equations yields the conclusion that several kinds of motion are actually achievable by the same 3-CPU architecture. Among them, pure rotational and pure translational mobilities are present. Finally, the existence of machine configurations allowing the transition between such modes is proved and the related poses are explicitly worked out.

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.

A novel bio-inspired modular gripper for in-hand manipulation

In the automation industry, in-hand manipulation is a frequently required task which needs a significant dexterity of grippers. Operations such as object twisting, re-grasp and repositioning with correct posture are the major challenges driving the gripper design and which determine its complexity. This paper proposes a new bio-inspired modular gripper which is capable to provide an object with motions of rotation about two independent axes. The proposed gripper is a modular device made of four identical fingers each one having two DOFs. Moreover, a proper mechanism was conceived to move two fingers out of four so as to ensure the grasping. In this research, the feasibility of the idea is proved by means of simulations in a multibody environment.

Impedance Control of a Spherical Parallel Platform

This article describes the impedance control of an in-parallel actuated orientation platform. The algorithm is based on a representation of platform orientation which exploits the equivalent axis of rotation: this approach is more intuitive and easier to visualize than conventional methods based on Cardan or Euler angles. Moreover, since for small angular displacements the Mozzis axis lies very close to angular velocity, impedance control algorithms based on such representation provides better performances and smoother motions. Results of numerical simulations and experimental tests are shown and commented with reference to the spherical parallel machine.