**2.2 Mechanical architecture of integrated systems**

As previously discussed the complexity of the general problem of creating the perfect illusion of touching a general object is still unsolved in the practice. However there are several device that are able to effectively reproduce a subset of fingertip physical interaction that generates artificial feeling of certain type of object properties.

On the Integration of Tactile and Force Feedback 53

The force that is exerted by the force feedback device to the user fingers have to be transmitted through a contact surface. In particular the way to transmit force has to take into account that the palmar side of the user finger surface is taken up by the tactile device. Such surface is than involved in the transmission of contact forces and the tactile array has to be

Several kinesthetic devices are equipped with force sensors that measure the interaction force at the level of the fingers of the user. The force signal is generally employed to compensate friction and inertia effects. The integration of a tactile feedback with the force sensor is a trivial problem since the vibration generated by the tactile transducer may

Arrays with high density are desirable but as the number of transducers to be driven

Processing electronics for controlling independently each actuator of a tactile array can be complex. For example a 5x5 array requires to independently control 25 current or voltage signals (depending from the actuation technology) over a bandwidth of 1-2 kHz. Moreover if we want to simplify the cabling this control electronics must should be placed as close as possible to the tactile display thus its dimension and weight must be reduced in order to minimize additional weight and inertia compensation forces for

The global problem of artificial creation of touch experience is too complex and a simplification can be made developing specific devices that are able to simulate only certain types of scenario. Basically, according to scenario, the device can be simplified in order to be optimized for a certain kind of application. Scenarios can be classified according to the complexity of the interaction starting from one finger interaction on a planar surface getting


The user can interact with an artificial surface moving on planar trajectories. According to the type of virtual surface, the speed and the forces exerted by the finger, the tactile display generates distributed stimulus. The kinaesthetic device can apply forces only on directions that are parallel to the plane and can simulate different macroscopic properties of the surface like friction or stiffness. Govindaraj in 2002 realize on planar system presenting a device able to simulate the interaction with a piece of fabric that is lying on a hard planar surface (Govindaraj et al., 2002). Another example of planar device has been realized by Yang(Yang & Zhang, 2009)

In the case of planar devices the requirements for the integration of tactile and kinesthetic displays are less demanding. The weight and the encumbrance of the tactile display are less

raises, the electrical cabling and the electronics get more and more complicated.

capable of sustaining such efforts without compromising its functionalities.

introduce a force noise reading (Fontana et al., 2007).

to spatial interaction with multiple fingers of the same hand:

scenario of integration of tactile and kinesthetic feedback.

that choose a cable-driven actuation system for the kinesthetic device.


Electronics and wiring

the kinesthetic stage.

**2.3.1 Scenario dependency** 



A possible idea for implementing a more general and flexible interface consists in designing a device that integrates together devices conceived for different scales.

The mechanical architecture of this kind of integrated device can be visualized as in Fig. 1. The system is composed by different layers:


This type of architecture can be found in many of the integrated haptic system that have been developed in (Frisoli et al., 2008), (Fontana et al., 2007),(Wagner et al., 2005) (Scilingo et al. 2010), (Sato et al.,2007).
