G. Boschetti, A.Trevisani, and V.Zanotto
Improving control design of haptic interfaces: a model for the users mechanical impedance
Accepted for publication in the 7th Int. Conf. ROBTEP 2004 - Automation / Robotics in theory and practice, Vysn Ruzbachy, Slovak Republic, May 2004.

Abstract: In a haptic system the human operator acts on an active mechanical device, which lets him sense and manipulate computer-generated or remote environments. A haptic interface is a tool which can convey information from a remote or virtual environment to operators’ fingers, hands or arms. The operator interacts with the interface by a variety of means, e.g. knobs, styli, handles or gloves. The interface hardware uses electrical servo-actuators to sense motion and/or forces generated by the user and to transmit feedback force signals to the operator. These forces are intended to convey information about the remote or virtual environment, ideally inducing in the user a sense of immersion in the remote or computer-generated world. From considerations arising in the control of haptic systems, an accurate dynamic modelling of the human hand grasping haptic devices could enhance the design of control laws and stability analysis. In particular, the fidelity of force transmission from the haptic interface to the user can be improved. In this way, it is possible to obtain an enhanced transparency of the haptic interface, which is one of the primary goals of the researches in this field. The stability of the overall haptic interface system is also an important issue. Unwanted oscillations and loss of control of the device not only reduce transparency, but can also pose a safety threat to the user. Stability depends on the user, on the device, on the external environment, and on the interactions among these three elements. Models characterizing the behaviour of the human mechanical impedance have already been presented in literature. Generally they are lumped linear time-invariant second-order models, often obtained using traditional system identification techniques. This paper develops a comprehensive characterization of the behaviour of the human mechanical impedance while manipulating a one degree of freedom haptic device. In particular, models for the human hand handling a haptic knob, models for the human finger and models for the human wrist are compared and discussed.

Area: Controllo di Sistemi Meccanici
Attività: HHI: Identificazione dell'impedenza meccanica della mano

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