Massimo Callegari

Kinematic Analysis of a Novel Translational Platform

A new three-d.o.f. parallel mechanism, with 3-RPC topology, is presented in the paper and its kinematics is studied. The proposed architecture, if proper geometrical conditions are satisfied, has an overconstrained structure which allows motions of pure translation. The simple structure of the mechanism allows finding closed-form solutions for both inverse and direct position kinematics; the differential analysis has been developed as well. by deriving a symbolic expression for the Jacobian matrix. Then, some design considerations are exposed to keep the singular points out of the working space of the mechanism and all the isotropic configurations are eventually identified.

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.

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.

Incremental Forming of Sheet Metal by Means of Parallel Kinematics Machines

The incremental forming of metal sheet parts can be an interesting alternative to the manual forging of the blanks or to the manufacturing of resin dies for the production of prototypes or small lots of parts. Indeed, the characteristics of small-volume production would call for an increase in the level of automation, possibly leading to a robotized cell able to complete the part after forming: in this case, the robot performing the deformation could automatically change its tools, cut the part, bend or flange the borders, load/unload the part, etc. Unfortunately, the conventional industrial robots do not have the required stiffness and are unable to apply the necessary forces to the blank. However, the rather new family of parallel robots has characteristics similar to machining centers, while still keeping the versatility of a robot. The present paper outlines the studies that have been performed at the Polytechnic University ofMarche in Ancona to assess the feasibility of the automated processing by using a hybrid robot interlocked to the incremental forming cell. The complexity of the experimental setup required the use of several simulation tools enabling off-line design of the experiments. In the end, an effective development environment has been set up, able to interface the different software tools in order to support the process designer in making the correct choices.

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.

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.

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.

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.