Matteo-Claudio Palpacelli

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.

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.

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.

Kinematics and optimization of the translating 3-CCR/3-RCC parallel mechanisms

The paper presents the kinematics of the 3-RCC/3-CCR translating parallel mechanisms and several machines of such family are described in detail taking into account different possible kinds of actuations. They all share good kinematic properties as for instance simple closed-form relations and convex workspace, but differ for overall dimensions of the mobile platform and dynamic behaviour: therefore the concepts have been optimized and compared against common performance indices, to determine the best solutions for selected classes of applications. Based on such results, a prototype robot has been finally built.

Simplified model for inverse dynamics control of the Cartesian parallel manipulator I.Ca.Ro.

This paper deals with the simulation of an inverse dynamics control scheme for a pure translational Cartesian parallel manipulator. Firstly, an analysis of robot dynamics is performed to verify the presence of poorly relevant terms. A polynomial simplified model is then built by fitting the mathematical model of the dynamics. The effectiveness of the proposed simplification is then tested through a simulated control scheme realized in a computer assisted modelling environment.

Design of a Bio-Inspired Autonomous Underwater Robot

The following paper presents the design and fabrication of an ostraciiform swimming robot and its navigation control and guidance system. Compared to other biomimetic vehicles, the chosen architecture has a lower propulsive efficiency but is easier to waterproof and capable to withstand greater pressures. To generate the alternating motion of the robot bio-inspired thruster, namely a plane fin, a transmission system was designed to replace the direct drive widely adopted in underwater biomimetic vehicles. The mechanical efficiency of two alternative mechanisms capable to actuate the fin were computed according to a preliminary sizing of the robot and its targeted swimming performances. Therefore, the more suitable solution was manufactured and installed aboard. At the same time, a proper navigation, guidance and control architecture (NGC) was designed and then integrated in the robot main controller. The proposed solution allows the vehicle to perform different missions autonomously once their profiles are received from the base station. Preliminary tests results and future works are discussed in the final conclusions.

Design and testing of a spherical parallel mini manipulator

The article describes the design, prototyping and preliminary testing of a miniaturized spherical parallel manipulator (SPM) with 2 DOFs of rotation, conceived to handle the orientation of a mobile platform during the assembly of very small components. The paper summarizes the basic equations of position and differential kinematics, and describes all the project phases for the realization of the first prototype. Furthermore, experimental data of preliminary tests are presented.