Pasquale Chiacchio

Closed-loop inverse kinematics schemes for constrained redundant manipulators with task space augmentation and task priority strategy

This article presents new closed-loop schemes for solving the inverse kinematics of constrained redundant manipula tors. In order to exploit the space of redundancy, the end- effector task is suitably augmented by adding a constraint task. The success of the technique is guaranteed either by specifying the constraint task ad hoc or by resorting to a task priority strategy. Instead of previous inverse kinemat ics schemes that use the Jacobian pseudoinverse, the schemes in this work are shown to converge using the Jacobian transpose. A number of case studies illustrate different ways of solving redundancy in the context of the proposed schemes.

Global task space manipulability ellipsoids for multiple-arm systems

New definitions of force and velocity manipulability ellipsoids for multiple-arm systems are given. A suitable kinetostatic formulation for multiple cooperating arms is adopted that allows a global task space description of external and internal forces as well as absolute and relative velocities at the object level. The concept of a force manipulability ellipsoid for a single arm is formally extended to the multi-arm case by regarding the whole system as a mechanical transformer from the extended joint space to the global task space. Kinetostatic duality properties are then exploited to derive velocity manipulability ellipsoids for the multiple-arm system. The proposed method is compared with other approaches using numerical examples. >

Six-DOF Impedance Control of Dual-Arm Cooperative Manipulators

In this paper, the problem of impedance control of dual-arm cooperative manipulators is studied. A general impedance control scheme is adopted, which encompasses a centralized impedance control strategy, aimed at conferring a compliant behavior at the object level, and a decentralized impedance control, enforced at the end-effector level, aimed at avoiding large internal loading of the object. Remarkably, the mechanical impedance behavior is defined in terms of geometrically consistent stiffness. The overall control scheme is based on a two-loop arrangement, where a simple proportional integral derivative inner motion loop is adopted for each manipulator, while an outer loop, using force and moment measurements at the robots wrists, is aimed at imposing the desired impedance behaviors. The developed control scheme is experimentally tested on a dual-arm setup composed of two 6-DOF industrial manipulators carrying a common object. The experimental investigation concerns the four different controller configurations that can be achieved by activating/deactivating the single impedance controllers.

Robust design of independent joint controllers with experimentation on a high-speed parallel robot

A linear independent joint control scheme is proposed. The design is made robust by closing another feedback loop that uses acceleration information besides the typical position and velocity loops. Reconstruction of acceleration measurements is performed via a suitable state-variable filter. Linear feedforward compensation is used to improve tracking performance of the closed-loop scheme. The control algorithm is tested first in a discrete-time simulation on a single-joint drive system with imposed disturbance torques. Then, real-time implementation on a high-speed parallel robot is presented. The experimental results demonstrate the effectiveness of the proposed technique. >

Direct and Inverse Kinematics for Coordinated Motion Tasks of a Two-Manipulator System

A new formulation for direct kinematics of a system of two manipulators is presented. This allows a straightforward description of general coordinated motion tasks in terms of meaningful absolute and relative variables. An effective inverse kinematics algorithm is devised which exploits the above formulation where the task Jacobians are expressed in terms of the Jacobians of the single manipulators. The scheme is extended to handle the presence of redundant degrees of freedom in the system. Different types of grasp between the end effectors and a commonly held object are treated with minimum reformulation effort. Case studies are developed throughout the paper for system of two PUMA 560 manipulators which illustrate the capabilities of the scheme.

Identification of dynamic parameters and feedforward control for a conventional industrial manipulator

Abstract Dynamic compensation control algorithms can improve the performance of conventional industrial manipulators if an accurate dynamic model is available. Usually, the structure of the dynamic model is known but the actual values of the dynamic parameters are either unknown or not accurately known. It is thus required to perform an identification of these parameter using available algorithms. In this paper, feedforward model-based control is experimented on a conventional industrial robot, the SMART-3 6.12R by COMAU, based on a dynamic parameter identification. Despite the fact that the conditions for the experiments are far from those provided by research set-ups, the obtained results have confirmed that it is worth using feedforward compensation control, either in a complete or in a partial form, even on an industrial set-up.

Aerial service robotics: The AIRobots perspective

This paper presents the main vision and research activities of the ongoing European project AIRobots (Innovative Aerial Service Robot for Remote Inspection by Contact, www.airobots.eu). The goal of AIRobots is to develop a new generation of aerial service robots capable of supporting human beings in all those activities that require the ability to interact actively and safely with environments not constrained on ground but, indeed, airborne. Besides presenting the main ideas and the research activities within the three-year project, the paper shows the first technological outcomes obtained during the first year and a half of activity.

Influence of Gravity on the Manipulability Ellipsoid for Robot Arms

The dynamic manipulability ellipsoid is a common tool in robotics to measure the ability of a manipulator to produce arbitrary accelerations of the end-effector for a given set of torques at the joints. This article is intended to demonstrate that for a robot arm, when gravitational forces (due to arm and payload) are properly embedded into the derivation of the ellipsoid, these do not cause a compression in the volume of the ellipsoid, as stated in the original approach, but they just produce a translation of the ellipsoid which is general occurs along all task space directions

Reformulation of dynamic manipulability ellipsoid for robotic manipulators

A reformulation of the dynamic manipulability ellipsoid for robotic manipulators is established. This ellipsoid is a common tool in robotics for measuring the ability of a manipulator to produce arbitrary accelerations of the end effector for a given set of torques at the joints. As opposed to the original approach where gravitational forces were imputed to compress the volume of the ellipsoid, it is shown that the effect of gravity can be taken into account by translating the center of the ellipsoid without affecting its volume. The ellipsoid for redundant manipulators is characterized by investigating the properties of the manipulator Jacobian involved in the core of the ellipsoid. Numerical case studies are developed.<<ETX>>

Coping with joint velocity limits in first-order inverse kinematics algorithms: analysis and real-time implementation

A major problem in inverse kinematics algorithms is that the generated joint velocities to be fed to the joint servos may cause violation of the speed limits of the joint actuators. In this paper, it is shown how to properly cope with joint velocity limits in first-order inverse kinematics algorithms; the proposed technique guarantees tracking of the desired end-effector path. This goal is achieved by suitably slowing down the task-space trajectory when joint velocity limits are encountered. The time law is modified through a time warp such that the introduced virtual time allows fulfillment of the velocity constraints. A case study is developed to show the effectiveness of the proposed method and a kinematic control scheme based on the presented technique is implemented to demonstrate feasibility under real-time constraints.