Paolo Gallina

Manipulability of a planar wire driven haptic device

This paper presents a planar 4 wire driven 3-DOF mechanism. For a planar haptic interface, this device could provide planar forces and moment feedback to the human operator. The particular end-effector geometric configuration overcomes manipulability problems arising from other recent planar wire haptic interfaces [R.L. Williams II, Int. J. Virtual Reality 3 (3) (1998) 13]. Moreover, an explicit forward kinematic pose solution is obtained by introducing a modified wire configuration. Complete kinematic and manipulability analyses are presented.

Planar Cable-Direct-Driven Robots: Design for Wrench Exertion

Cable-direct-driven robots and haptic interfaces are appealing because of their structural simplicity, high stiffness, and high exerted wrench-to-weight ratio. A major drawback is that cables can only exert tension. Therefore, actuation redundancy is required to apply general wrenches (force/moment vectors). Even with actuation redundancy, not all desired wrenches can be applied in some configurations due to one or more negative cable forces required. In addition, cable interference can be a serious problem for these devices. The objective of this article is to present the best design for planar cable-direct-driven robots and/or haptic interfaces with one degree of actuation redundancy, with regard to general wrench exertion and cable interference. Results indicate that the cable interference constraint dominates which suggests the need for future design work to alleviate this interference.

3-d.o.f. Wire Driven Planar Haptic Interface

A 4-wire driven 3-d.o.f. planar haptic device, called the Feriba-3, is described. The particular geometric configuration of the end-effector ensures a closed form kinematic pose solution and good manipulability. Moreover, the structural arrangement adopted makes the Feriba-3 a well-performing haptic device, whose major features are low inertia, low friction, and full dexterity in a large workspace. The manipulability analysis has been performed by introducing a complete set of manipulability indices.

Upper limb rehabilitation robotics after stroke: a perspective from the University of Padua, Italy.

Rehabilitation robotics is an emerging research field that aims to employ leading-edge robotic technology and virtual reality systems in the rehabilitation treatment of neuro-logical patients. In post-stroke patients with upper limb impairment, clinical trials have so far shown positive results in terms of motor recovery, but poor efficacy in terms of functional outcome. Much work is needed to develop a new generation of rehabilitation robots and clinical protocols that will be more effective in helping patients to regain their abilities in activities of daily living. This paper presents some key issues in the future perspective of upper limb robotic rehabilitation after stroke.

A Technique to Analytically Formulate and to Solve the 2-Dimensional Constrained Trajectory Planning Problem for a Mobile Robot

A new technique for trajectory planning of a mobile robot in a two-dimensional space is presented in this paper. The main concept is to use a special representation of the robot trajectory, namely a parametric curve consisting in a sum of harmonics (sine and cosine functions), and to apply an optimization method to solve the trajectory planning problem for the parameters (i.e., the coefficients) appearing in the sum of harmonics. This type of curve has very nice features with respect to smoothness and continuity of derivatives, of whatever order. Moreover, its analytical expression is available in closed form and is very suitable for both symbolic and numerical computation. This enables one to easily take into account kinematic and dynamic constraints set on the robot motion. Namely, non-holonomic constraints on the robot kinematics as well as requirements on the trajectory curvature can be expressed in closed form, and act as input data for the trajectory planning algorithm. Moreover, obstacle avoidance can be performed by expressing the obstacle boundaries by means of parametric curves as well. Once the expressions of the trajectory and of the constraints have been set, the trajectory planning problem can be formulated as a standard mathematical problem of constrained optimization, which can be solved by any adequate numerical method. The results of several simulations are also reported in the paper to show the effectiveness of the proposed technique to generate trajectories which meet all requirements relative to kinematic and dynamic constraints, as well as to obstacle avoidance.

WHEELED OMNI-DIRECTIONAL ROBOT DYNAMICS INCLUDING SLIP

A dynamic model is presented for omni-directional wheeled mobile robots, including wheel/motion surface slip. We derive the dynamics model, experimentally measure friction coefficients, and measure the force to cause slip (to validate our friction model). Dynamic simulation examples are then presented to demonstrate omni-directional motion with slip. After developing an improved friction model, compared to our initial model, the simulation results agree well with experimentally-measured trajectory data with slip. Initially we thought that only high robot velocity and acceleration governed the resulting slipping motion. However, we learned that the solid material existing in the discontinuities between omni-directional wheel rollers plays an equally important role in determining omni-directional mobile robot dynamic slip motion, even at low rates and accelerations.Copyright

Design of a PID Controller for a Flexible Five-Bar Closed-Chain Planar Manipulator

This paper presents the design of a PID controller for a flexible planar manipulator, based on a very accurate dynamic model of the system. The model is employed to test a classical PID regulator in simulation, in order to be able to control a flexible five-bar closed-chain planar manipulator. The chosen PID controller is described, and the most significant simulation results are presented and discussed.

Development of a state-space water-level control for an array of cells to be employed as compensator in radiotherapy

This paperdeals with the problem of water-level control for an array ofcells by means of an hydraulic circuit. An on-off valve fillsall the cells, while each cell is drained by a single on-offvalve, so the control is intrinsically coupled. An optimal controlwith PWM (pulse width modulation) valves is carried out. At theend, simulation and experimental results are presented. The arrayof cells may find application as compensator for radiotherapy(Total Body Irradiation), by interposing the cells between thex-ray source and the patient: on-line water-level variationsin the cells allow local radiation dose control.

Admittance Model Haptic Interaction for Large Workspace Teleoperation

This paper presents a control method for scaled teleoperation where the slave workspace is larger than the master one. In future, the results of this paper will be employed in a joystick for excavator controlling. The whole system is made up of a haptic master device and a virtual slave one. The master device consists in an 1 D.o.F. joystick provided with a shaft mounted torque sensor. The scaled force the human operator exerts on the master device commands the slave device input force. Conversely, the master position follows the slave position. In this way, a realistic feeling of the remote environment is provided. A virtual damping force proportional to the slave speed is introduced into the slave control in order to improve the teleoperation. The theoretical approach has been validated with experimental results.

A Catadioptric System for 3-D Optical Measurements

In this paper we describe the feasibility analysis and the prototyping of a 3-D optical measurement system. The system is a catadioptric one, consisting of a combination of refracting (camera lens) and reflecting (mirror) elements. Employing mirrors in order to increase efficiency in camera CCD exploitation, is the innovative idea we propose. An accurate study of camera calibration and distortion correction algorithm have been carried out. Moreover, we propose a closed-form solution for camera calibration. This method has been integrated with the Newton-Raphson algorithm. Eventually, experimental results are given.