Generation of Stimuli Supporting Tactile Perception of Textiles in a VR System

Den­nis Al­ler­kamp, Leib­niz Uni­ver­si­tät Han­no­ver

Vir­tu­al Rea­li­ty has a lot of ap­p­li­ca­ti­ons ran­ging from en­ter­tain­ment to me­cha­ni­cal de­sign and me­di­cal trai­ning. With the ap­pearan­ce of vir­tu­al worlds where users can in­ter­act via ava­tars over the In­ter­net (e.g. Se­cond Life), com­pa­nies star­ted to pro­mo­te their pro­ducts as vir­tu­al ar­te­facts – ano­ther emer­ging ap­p­li­ca­ti­on of Vir­tu­al Rea­li­ty. Vir­tu­al rea­li­ty sys­tems can be ca­te­go­ri­sed by the mo­da­li­ties they sup­port. In today's sys­tems the mo­da­li­ties of see­ing and hea­ring are the most com­mon­ly em­ploy­ed as these are also the mo­da­li­ties in which we as human beings most­ly ex­ch­an­ge in­for­ma­ti­on. They re­qui­re least ef­fort in terms of en­er­gy trans­fer, the cor­re­spon­ding sen­so­ry re­cep­tors are con­cen­tra­ted in the re­ti­na and the co­ch­lea and can be ex­ci­ted re­mo­te­ly with light and sound waves re­spec­tive­ly.

In con­trast to see­ing and hea­ring the crea­ti­on of ap­pro­pria­te hap­tic sti­mu­li de­man­ds very so­phis­ti­ca­ted hard­ware. First­ly, the skin with its size of 1.5 to 2 squa­re me­ters is a very large organ. The­re­fo­re most hap­tic de­vices focus on a ra­ther small part of the human body – usual­ly the fin­ger­tip. Se­cond­ly, forces can­not be trans­mit­ted con­tact-free with cur­rent tech­no­lo­gy. Thus hap­tic de­vices al­ways need di­rect con­tact to the parts of the skin where the forces are ap­p­lied. Third­ly, the amount of en­er­gy is re­la­tive­ly high com­pa­red to other mo­da­li­ties, e.g. if one wants to si­mu­la­te the lif­ting of an ob­ject with a mass of 500 g the hap­tic de­vice has to crea­te a force of ap­pro­xi­mate­ly 5 N. All these pro­per­ties make hap­tic si­mu­la­ti­on a com­plex task still pre­sen­ting a lot of pro­blems await­ing a good so­lu­ti­on. But these ef­forts will re­sult in a ri­cher, more con­vin­cing vir­tu­al rea­li­ty ma­king ap­p­li­ca­ti­ons like the pro­mo­ti­on of tex­ti­les via the In­ter­net pos­si­ble.

Most hap­tic de­vices focus on the trans­mis­si­on of forces as this is the most strai­ght­for­ward ap­proach to si­mu­la­te the hap­tic pre­sence of an ob­ject. These forces are usual­ly ex­er­ted on the fin­ger­tip via a sim­ple thim­ble, dis­re­gar­ding the ac­tu­al force dis­tri­bu­ti­on on the con­tact area bet­ween fin­ger­tip and ob­ject. This is com­pa­ra­ble to the hap­tic in­ter­ac­tion with real ob­jects using a real thim­ble. As­ses­sing small sur­face fea­tures or sur­face rough­ness is very hard or even im­pos­si­ble in this way. Using a tac­ti­le dis­play is a pos­si­bi­li­ty to over­co­me this short­co­m­ing.

In this pro­ject a tac­ti­le dis­play de­ve­l­o­ped at the Bio­me­di­cal Phy­sics Group of the Uni­ver­si­ty of Exe­ter will be em­ploy­ed. It con­sists of an array of 24 pins that are dri­ven by vi­bra­ting pie­zo­electric bi­morphs. These pins are in­ten­ded to pro­du­ce vir­tu­al touch sen­sa­ti­ons by crea­ting an ap­pro­pria­te spa­tio­tem­po­ral va­ria­ti­on of me­cha­ni­cal dis­tur­ban­ce over the skin of the fin­ger­tip. The prin­ci­pal topic of the pro­po­sed pro­ject is the se­arch for such a spa­tio­tem­po­ral va­ria­ti­on that re­sem­bles the touch sen­sa­ti­on of a fin­ger mo­ving over the sur­face of a real tex­ti­le.

Va­rious sub­tasks have to be ad­dres­sed:

  • mea­su­re­ment and ana­ly­sis of real fa­brics' sur­faces
  • crea­ti­on of a da­ta­ba­se of vir­tu­al fa­brics cor­re­spon­ding to real fa­brics
  • de­ve­lop­ment of an elec­tro­nic sys­tem ca­pa­ble of ge­ne­ra­ting ap­pro­pria­te electri­cal si­gnals dri­ving the pie­zo­electric bi­morphs of the tac­ti­le dis­play
  • sur­vey of exis­ting psy­cho­phy­si­cal stu­dies re­la­ted to human tac­ti­le per­cep­ti­on in ge­ne­ral and the tac­ti­le ren­de­ring of fa­brics in par­ti­cu­lar
  • de­ve­lop­ment and im­ple­men­ta­ti­on of pro­mi­sing tac­ti­le ren­de­ring stra­te­gies
  • eva­lua­ti­on and com­pa­ri­son of tac­ti­le ren­de­ring stra­te­gies.

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