Nicola Diolaiti

Stability of Haptic Rendering: Discretization, Quantization, Time Delay, and Coulomb Effects

Rendering stiff virtual objects remains a core challenge in the field of haptics. A study of this problem is presented, which relates the maximum achievable object stiffness to the elements of the control loop. In particular, we examine how the sampling rate, quantization, computational delay, and amplifier dynamics interact with the inertia, natural viscous, and Coulomb damping of the haptic device. Nonlinear effects create distinct stability regions, and many common devices operate stably, yet in violation of passivity criteria. An energy-based approach provides theoretical insights, supported by simulations, experimental data, and a describing function analysis. The presented results subsume previously known stability conditions

Contact impedance estimation for robotic systems

In this paper, the problem of online estimation of the mechanical impedance during the contact of a robotic system with an unknown environment is considered. This problem is of great interest when controlling a robot in an unstructured and unknown environment, such as in telemanipulation tasks, since it can be easily shown that the exploitation of the knowledge of the mechanical properties of the environment can greatly improve the performance of the robotic system. In particular, a single-point contact is considered, and the (nonlinear) Hunt-Crossley model is taken into account, instead of the classical (linear) Kelvin-Voigt model. Indeed, the former achieves a better physical consistency and also allows describing the behavior of soft materials. Finally, the online estimation algorithm is described and experimental results are presented and discussed.

Teleoperation of a mobile robot through haptic feedback

Teleoperation systems have been developed in order to allow a human operator to perform complex tasks in remote environments. Mobile robots can be considered as a particular example of telemanipulation systems, since they can be operated remotely to perform particular tasks. As an example, the inspection of underwater structures and the removal of mines are performed by mobile platforms controlled by a remote operator, which generally takes advantage only of the visual feedback provided by vision systems. In this sense, the nature and completeness of the data provided to the operator about the state of the remote system are of crucial importance for proper task execution, and it is generally accepted that a more efficient achievement of the task can be obtained by increasing the amount of data feedback and using proper MMI. In this paper, the use of a haptic interface is proposed in order to increase a users perception of the workspace of a mobile robot. In particular, a virtual interaction force is computed on the basis of obstacles surrounding the mobile vehicle in order to prevent dangerous contacts, so that navigation tasks can be carried out with generally better performances. In addition, passivity of the overall system is taken into account, so that stability of the virtual interaction is guaranteed.

The effect of quantization and Coulomb friction on the stability of haptic rendering

Rendering stiff virtual objects remains a core challenge in the field of haptics. A study of this problem is presented, which relates the maximum achievable object stiffness to the elements of the control loop. In particular, we examine how the sampling rate and quantization of position measurements interact with the inertia, natural viscous, and Coulomb damping of the haptic device. The resulting stability criterion generalizes previously known conditions. Simulations and experimental results support the theoretical analysis based on the passivity and describing function approaches.

A Criterion for the PassivitY of Haptic Devices

Rendering a stiff virtual wall remains a core challenge in the field of haptics. A passivity study of this problem is presented, which relates the maximum achievable wall stiffness to the system discretization and sampling delays, to the quantization of the encoder, to the inertia of the haptic device, as well as to both the natural viscous and Coulomb damping present in the haptic device. The resulting stability criterion generalizes previously known results. Its analytic derivation is verified in both simulation and experiments on a one degree of freedom testbed.

Haptic tele-operation of a mobile robot

Abstract Teleoperation systems have been developed in order to allow a human operator to perform complex tasks in remote environments. Mobile robots can be considered as a particular example of telemanipulation systems, since they can be operated remotely to perform particular tasks. As an example, the inspection of underwater structures and the removal of mines are performed by mobile platforms controlled by a remote operator, which generally takes advantage only of the visual feedback provided by vision systems. In this paper, the use of a haptic interface is proposed in order to increase the users perception of the workspace of the mobile robot. In particular, a virtual interaction force is computed on the basis of obstacles surrounding the mobile vehicle in order to prevent dangerous contacts. The passivity of the overall system is preserved, so that stability of the virtual interaction is guaranteed.

Wave Haptics: Providing Stiff Coupling to Virtual Environments

Traditional haptic rendering creates virtual springs using DC motors with current amplifiers and encoder-based position feedback. In these schemes, quantization, discretization, and amplifier bandwidth all impose performance limits. Meanwhile the amplifiers try to cancel the motor’s electrical dynamics, though they are actually beneficial to the haptic display. We present an alternate approach that fully embraces and utilizes all electrical dynamics, following two insights. First, the electrical inductance L can serve as a stiffness, providing a natural sensor-less elastic coupling between the virtual environment and the user. Second, we take advantage of the electrical resistance R to compute, by means of analog circuitry, a wave transform. Implementing virtual objects in a wave domain provides robustness to servo delays or discretization. The resulting system requires only a simple voltage drive circuit. Built upon the motor’s physical behavior, it can outperform traditional approaches, achieving higher virtual stiffness. Encoder feedback is only required for absolute position information, with damping and velocity information inherently available from back-EMF effects. A prototype 1-DOF system has been implemented and confirms the promise of this novel paradigm.