Modeling VR-systems for haptic interaction with mechanical objects especially textiles

Guido Bött­cher, Leib­niz Uni­ver­si­tät Han­no­ver

In the past de­ca­des com­pu­ter gra­phics has be­co­me an es­sen­ti­al part in sci­ence as it pro­vi­des al­go­rithms and me­thods hel­ping to vi­sua­li­se pro­blems and pro­ces­ses in dif­fe­rent fiel­ds of re­se­arch. For ex­amp­le, in wea­ther fo­re­casts, mo­dels are used to si­mu­la­te the dy­na­mics of the at­mo­s­phe­re and its in­ter­ac­tion with seas and land mas­ses. Wi­thout an ade­qua­te vi­sua­li­sa­ti­on of the huge data sets pro­du­ced by the mo­dels, it is very hard to make a fo­re­cast re­ly­ing on the com­pu­ted data. 

By gi­ving the user a vi­su­al re­pre­sen­ta­ti­on of the com­pu­ter-ge­ne­ra­ted out­put it is pos­si­ble to in­stant­ly un­der­stand what has been com­pu­ted and how it is re­la­ted to a sta­ted pro­blem. This ap­proach has been dri­ven fur­ther to a level where the user is com­ple­te­ly sur­roun­ded by a vir­tu­al en­vi­ron­ment which re­sem­bles rea­li­ty. Spe­cial ste­reo­sco­pic dis­plays crea­te a true three di­men­sio­nal view that is per­fec­ting the il­lu­si­on to be fully im­mer­sed in this so-cal­led Vir­tu­al Rea­li­ty (VR). 

While the gra­phi­cal ren­de­ring of Vir­tu­al En­vi­ron­ments is more and more in­dis­tin­gu­is­ha­ble from real images, the in­ter­ac­tion in­si­de such a world is quite far away from being rea­lis­tic. Se­veral as­pects in the in­ter­ac­tion bet­ween user and VR are still mis­sing. The most im­portant as­pect is the hap­tic fee­ling when a user is in con­tact with an ob­ject. Even though we rely main­ly on the vi­su­al sense we still need the sen­sa­ti­on of tou­ch­ing an ob­ject. Other­wi­se we could not in­tui­tive­ly grasp and ma­ni­pu­la­te in­si­de the VR. Mo­re­o­ver, we have to feel the in­ter­ac­tion forces oc­cur­ring at the con­tact. Ge­ne­ral­ly spea­king, when we grasp an ob­ject we have an en­er­gy trans­fer from the user to the ob­ject and vice versa. To crea­te a con­vin­cing im­pres­si­on of a real touch such trans­fers have to be ad­dres­sed ap­pro­pria­te­ly. That means we have to con­sider the ef­fect of the en­er­gy trans­fer in the me­cha­ni­cal be­ha­viour of the tou­ched ob­ject with re­spect to the un­der­ly­ing ma­te­ri­al. In case of a rigid ob­ject cau­sing a chan­ge of po­ten­ti­al and ki­ne­tic en­er­gy, the trans­fer is vi­si­ble in the mo­ti­on, whe­re­as for a soft body , it re­sults in a de­for­ma­ti­on under the load the user ap­p­lies at the con­tact. A VR-Sys­tem ca­pa­ble of dea­ling with such phy­si­cal pro­ces­ses has to make sure that it de­li­vers the con­tact forces at a very high up­date rate (ap­prox. 1 kHz). This is a ge­ne­ric re­qui­re­ment for achie­ving a high fi­de­li­ty hap­tic sen­sa­ti­on in the in­ter­ac­tion. 

As the afo­re­men­tio­ned con­side­ra­ti­ons are in the whole a de­man­ding task for cur­rent com­pu­ter sys­tems and many of today's VR-sys­tems sim­pli­fy the in­ter­ac­tion to some extent. Their pos­si­bi­li­ties are eit­her li­mi­ted to sin­gle con­tact points (no grasping pos­si­ble) or to con­tacts of low fi­de­li­ty by ha­ving only ac­cu­ra­te force up­dates of a few Hertz. 

The aim of the pro­ject is the­re­fo­re to de­ve­lop a VR-sys­tem that is able to crea­te a link bet­ween si­mu­la­ti­ons that can com­pu­te phy­si­cal­ly cor­rect de­for­ma­ti­ons of ob­jects under load while ha­ving a high rate up­date in the con­tact force. Ad­di­tio­nal­ly, it should con­sider the in­ter­ac­tion of two fin­gers wi­t­hin the vir­tu­al en­vi­ron­ment. A spe­cial case of ap­p­li­ca­ti­on should be the hap­tic sen­sing of con­tact forces bet­ween the fin­gers and vir­tu­al tex­ti­les. It should be pos­si­ble for a user to grasp and touch a piece of fa­bric. Under these con­di­ti­ons spe­cial al­go­rithms have to be de­ve­l­o­ped that are not only able to re­pro­du­ce the high­ly dy­na­mic be­ha­viour of tex­ti­les but also ca­pa­ble of ac­cu­ra­te­ly com­pu­ting the small forces (order of few grams) at the con­tact point.

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showing an actual screenshot of the VR-system software

the complete VR-system of the HAPTEX Project operated by a user