**4.2.1 Kinesthetic and tactile stages conceived for integration**

As briefly analyzed in the previous section multi-finger interaction is the most demanding and complex scenario. However it is also the most versatile application of haptics and the potential application fields are extremely wide. One of the most relevant aspects of the design of an integrated tactile/kinaesthetic display is to guarantee at the same time:


In the present case study we introduce an example of design for integration where both tactile display and kinaesthetic devices were conceived for the integration. In particular a new transducer for the realization of a tactile display was purposely developed for the integration with an dual finger hand-exoskeleton.

The exoskeleton device is a dual arm serial manipulator able to deliver accurate forces in the range of 5N on the fingertip of the index and thumb fingers the device is shown in Fig. 4 and presented in detail in (Fontana et al., 2009). The architecture and the mechanical solutions for the exoskeleton have been studied in order to enhance performances and allow the hosting of a tactile display. The main characteristics can be summarized in table 1. The HE has been integrated in the work described in (Fontana et al., 2007) with tactile display based on piezo-electric beam that was purposely developed for the integration by Univeristy of Exeter. The system was integrated system was successfully tested on a scenario for virtual textile haptic simulation.

Despite of the effort applied for realizing a compact tactile display the system shows limitations in usability. Bulky shape of the display and wiring were determined by the basic principle. The piezo-beam actuators require a minimum length of few centimetres for each beam to guarantee a sufficient displacement of the contact pin.

A second tactile display has been studied focusing on compact electromagnetic actuators. The system described in (Salsedo et al., 2011) is based on a solenoid transducer that was designed for optimal force-displacement versus encumbrance performances.

As briefly analyzed in the previous section multi-finger interaction is the most demanding and complex scenario. However it is also the most versatile application of haptics and the potential application fields are extremely wide. One of the most relevant aspects of the

In the present case study we introduce an example of design for integration where both tactile display and kinaesthetic devices were conceived for the integration. In particular a new transducer for the realization of a tactile display was purposely developed for the

The exoskeleton device is a dual arm serial manipulator able to deliver accurate forces in the range of 5N on the fingertip of the index and thumb fingers the device is shown in Fig. 4 and presented in detail in (Fontana et al., 2009). The architecture and the mechanical solutions for the exoskeleton have been studied in order to enhance performances and allow the hosting of a tactile display. The main characteristics can be summarized in table 1. The HE has been integrated in the work described in (Fontana et al., 2007) with tactile display based on piezo-electric beam that was purposely developed for the integration by Univeristy of Exeter. The system was integrated system was successfully tested on a

Despite of the effort applied for realizing a compact tactile display the system shows limitations in usability. Bulky shape of the display and wiring were determined by the basic principle. The piezo-beam actuators require a minimum length of few centimetres for each

A second tactile display has been studied focusing on compact electromagnetic actuators. The system described in (Salsedo et al., 2011) is based on a solenoid transducer that was

design of an integrated tactile/kinaesthetic display is to guarantee at the same time:

Fig. 3. General architecture of the mechanical interface

**4.2.1 Kinesthetic and tactile stages conceived for integration** 



beam to guarantee a sufficient displacement of the contact pin.

designed for optimal force-displacement versus encumbrance performances.

**4.2 Hand exos and custom tactile array** 


integration with an dual finger hand-exoskeleton.

scenario for virtual textile haptic simulation.

Fig. 4. PERCRO Dual finger Exoskeleton with 3 DoF for each finger able to deliver 5N on the fingertip of index and thumb. The device was purposely developed for the haptic interaction with textiles and for the integration with a tactile display.


Table 1. Mechanical performances of the hand-exoskelton

The transducers were arranged in an array of 5x6 with a spacing of 2.4 mm with 4mm of thickness (Fig. 5).

Fig. 5. Scheme of the integration of tactile display with the hand exoskeleton

On the Integration of Tactile and Force Feedback 65

During the ON phase, the transfer function which expresses the coil current respect to the

 <sup>2</sup> 00 0

*<sup>V</sup> R LCs R RC L s R R*

in which the typical MOSFET on-resistance is considered inside the term R0. The natural

; <sup>0</sup>

1 *ON OFF L R RC*

A necessary condition for limiting the variation of current through the coil during a PWM cycle is to dimension the capacitor C and the resistor R0 imposing a time constants of the

Assuming that this requirement is satisfied, it's possible to find a simplified relation between the coil current and the duty cycle of the PWM signal. Making the assumption that *VC* is a constant voltage applied to the capacitor, the current *iC* flowing into the capacitor

> 0 *CC C C*

*R R* 

> 0 1 *CC C C*

*OFF OFF <sup>V</sup> Q T C R* ;

1 *<sup>C</sup>*

*V VV <sup>i</sup>*

*V VV Q T CR R* 

Indicating with α and *TPWM* respectively the duty cycle and the period of the PWM signal,

*T T T T* 

 1 *ON PWM OFF PWM*

When the frequency content of variation of the imposed average current is much lower than the PWM frequency we can assume that the charge during the two phases are identical. We

*R R*

 

*R C L* 2

.

*L R*

0

;

*L R RC R R*

*OFF*

1

;

1 *ON OFF*

 

0 1

;

,

supply voltage is the following

1

; 2 *OFF*

1 *<sup>L</sup>*

*n OFF LC*

*CC I*

<sup>0</sup> , , 1

OFF phase circuits larger enough than the period of the PWM cycle.

,

*ON ON*

, *<sup>C</sup> C OFF <sup>V</sup> <sup>i</sup> <sup>R</sup>* ;

can than calculate the duty cycle for obtaining an average coil current *iL* :

During the OFF phase, the above quantities can be expressed as follow

*C ON*

1 *n ON n OFF*

frequency, the damping ratio and the time constant are:

 

during the ON phase is given by

The supplied electrical charge can be written as:
