During the first months of the TACTILITY project, as part of task T2.3, TECNALIA has manufactured and validated the Alpha prototype of the TACTILITY stimulator, which is already operational and will be used for the initial research activities regarding the electro-tactile feedback. This initial integration for the Alpha system will be used for different demonstrations of the capabilities of TACTILITY.
The stimulation hardware unit supports distributed stimulation over multi-pad electrodes and has been designed based on specifications for the desired electrotactile stimuli, the defined electrode sizes, shapes and layouts. The stimulation system includes a DC/DC converter that ensures stable supply and high precision current control and will allow calibration of the afferent electrical stimuli over each electrode. The control unit of the stimulation stage allows in addition to the high precision control of current amplitude and fine-tuning of the pulse width of each pulse. The other parameter is the stimulation frequency, which is important for the type of feedback sensation. The integrated demultiplexing circuitry enables distribution of each individual pulse to any pad of the up to 32 channel multifield electrode of the Alpha prototype.
As shown in the block diagram the TACTILITY stimulator consists of a control board that handles supply, communication and storage and in addition controls the pulse generation. The pulse is later demultiplexed to the different channels to be transmitted to the skin by the multifield electrode.
The TACTILITY stimulator is using spring-loaded connectors to interface with the multifield electrodes. These connectors assure continuous and reliable contact to the 32 electrotactile stimulation channels.
The TACTILITY stimulator can generate asynchronous biphasic symmetrical or biphasic compensated stimulation pulses. The main stimulation parameters are shown in the following table.
|Electrotactile stimulation configurable parameters|
|Number of fields||32 (configurable as not used, active or return)|
|Frequency||1 – 200 Hz|
|Intensity||0.1 – 9 mA (1kΩ)|
|Pulse width||30 – 500 μs (1kΩ)|
|Pulse compensation||1 – 10|
Several TACTILITY partners used the system for their initial research on the electrotactile feedback. An integration with the VR environment for demonstrations of TACTILITY’s current and future capabilities has been completed.
The Beta version has a) a size reduction, b) an increase of the number of stimulation output channels and c) the integration of the device with the TACTILITY glove.
Components and first versions of the TACTILITY glove as part of the Beta version are shown in the pictures a)-d) below. Note that a dual glove solution was used comprising an inner glove with the transferred electrodes connected to the stimulator and an outer glove with the kinematic sensors.
A couple of virtual reality (VR) scenarios were implemented to showcase the functionality of the system. The next picture is a screenshot from the automotive scenario.
The second demonstrator, a virtual forest in which it is raining, showed potential functionalities related to the full hand stimulation and the capability of providing stimulation and its precise localization on the palm of the user’s hand simulating the sensation of raindrops falling on the user’s hand.