Traditional haptic rendering creates virtual springs using DC motors with current amplifiers and encoder-based position feedback. It is well known that the stiffness of virtual environments is limited by quantization, discretization, and amplifier bandwidth effects. In this paper we propose a novel control architecture that, rather than canceling motor electrical dynamics, uses them to achieve better performances. First we recognize that the inductance L provides a natural sensor-less stiff behavior at high frequencies. Second, electrical resistance R serves as the basis of a wave transform that, performed through an analog circuit, allows to build a more stable interface with virtual environments, achieving robustness to servo delays and discretization. Encoder feedback and digital control loop are required only to provide parametric robustness at low frequencies. A prototype 1-DOF system has been implemented and confirms the promise of this novel paradigm

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

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.

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.

In this paper, the problem of the on-line estimation of the mechanical impedance during the contact of a robotic system with an unknown environment is considered. Indeed, the knowledge of the mechanical properties could allow to improve the interaction between robotic devices and unstructured and unknown environments, e.g. in telemanipulation tasks. A single-point contact is considered and the (nonlinear) Hunt-Crossley model is taken into account and its better physical consistency in describing the behavior of soft materials is discussed in comparison with the classical (linear) Kelvin-Voigt model. Finally, the on-line estimation algorithm is described and experimental results presented.