Haptics: why give machines a sense of touch? 

Hap­tics. The word may sound com­plex, but the con­cept is sim­ple: it refers to any­thing relat­ed to the sense of touch. Many research teams around the world are not only try­ing to under­stand this sense, but also to repro­duce it – much like a cam­era repro­duces sight. 

This field of study is not new. “Hap­tic sen­sa­tion is a long-stand­ing sub­ject. Researchers have been try­ing to devel­op hap­tic sen­sors for forty years,” explains Kostas Danas, research direc­tor of the sol­id mechan­ics lab­o­ra­to­ry at École Poly­tech­nique (IP Paris) and the CNRS. 

We inter­act with one type of hap­tic tech­nol­o­gy every day: hap­tic feed­back, the feed­back giv­en to the user by a vibra­tion that stim­u­lates the sense of touch – like when a phone vibrates as you press a but­ton. Sim­i­lar­ly, it is this tech­nol­o­gy that is used in vir­tu­al real­i­ty gloves. 

While stim­u­lat­ing the sense of touch is com­mon in today’s tech­nol­o­gy, mak­ing hap­tic mate­r­i­al – that is, repro­duc­ing this sense – remains a chal­lenge. Since 2015, Kostas Danas and his team have been work­ing on a mate­r­i­al with these prop­er­ties. “It is a new type of very flex­i­ble mate­r­i­al: we make a com­pos­ite from a poly­mer into which we put par­ti­cles that are mag­neti­s­able,” con­tin­ues the researcher. “In par­tic­u­lar, we can use par­ti­cles that remain per­ma­nent­ly mag­ne­tised after the appli­ca­tion of a mag­net­ic field, which gives a flex­i­ble mag­net. These par­ti­cles come from the same type of mate­r­i­al as those used in con­ven­tion­al magnets.”

When you touch some­thing, the mate­r­i­al dis­torts, and the mag­net­ic field will change around it.

When the mag­net­ic field is applied, the mate­r­i­al will deform. Con­verse­ly, when it is deformed after being mag­ne­tised, it will act on the mag­net­ic field around it. It is these prop­er­ties and flex­i­bil­i­ty that give it its hap­tic char­ac­ter­is­tics. “When you touch some­thing, the mate­r­i­al will dis­tort, and the mag­net­ic field will change around it. This change will be mea­sur­able: we play with the alter­nat­ing mag­net­ic fields, fol­low­ing the defor­ma­tion, to mea­sure the touch,” explains Kostas Danas. This type of tech­nol­o­gy capa­ble of mea­sur­ing touch is called hap­tic sen­sors.

The pos­si­ble uses of these hap­tic sen­sors are diverse. The flex­i­bil­i­ty of the mate­r­i­al cre­at­ed makes it pos­si­ble to adapt to any form of robot. “Hap­tic sen­sors have appli­ca­tions in all areas where there are robots. At present, there are almost no robots that have this sense of touch. Cur­rent­ly, they only see with cam­eras,” explains Kostas Danas. But adding this sense to robots can have many dif­fer­ent uses, such as in the bio­med­ical field, for min­i­mal­ly inva­sive surgery¹. 

This type of surgery con­sists of per­form­ing an oper­a­tion through a small inci­sion and with the video-assis­tance, either with long instru­ments or on robots equipped with small cam­eras. But 2D video lim­its the pos­si­bil­i­ties of these robots: giv­ing them an addi­tion­al sense could great­ly increase their capa­bil­i­ties and the amount of infor­ma­tion they can return to the surgery. This would make more surg­eries eli­gi­ble for this type of oper­a­tion, which would be ben­e­fi­cial to med­i­cine, as min­i­mal­ly inva­sive surgery reduces both the risks involved and the recov­ery time after surgery. 

Anoth­er appli­ca­tion to be con­sid­ered in the bio­med­ical field con­cerns the assess­ment of tis­sue elas­tic­i­ty and its tac­tu­al explo­ration. This is usu­al­ly done today by the sur­geon with his or her bare hands and is extreme­ly impor­tant for find­ing arter­ies and tumours in the body, as well as deter­min­ing the qual­i­ty of the patient’s tis­sue. How­ev­er, doc­tors can some­times miss nod­ules and small bumps dur­ing their inspec­tion. Small robots with high­ly sen­si­tive hap­tic capa­bil­i­ties could there­fore assist sur­geons in this process, to ensure that every­thing is detected.

In par­tic­u­lar, the flex­i­bil­i­ty of the mate­r­i­al cre­at­ed makes it pos­si­ble to adapt to any form of robot. 

Final­ly, it is the pros­the­ses that could be equipped with hap­tic sen­sors. A per­son with a hand ampu­ta­tion could thus have hap­tic sen­sors in the fin­gers of the pros­the­sis, which would send sen­sa­tions through­out the hand. In addi­tion, hap­tic sen­sors should also be con­sid­ered to check the fit of the pros­the­sis when the per­son per­forms move­ments. Indeed, in the long term, with the dif­fer­ent move­ments of dai­ly life, a bad fit of the pros­the­sis can lead to many prob­lems in the con­cerned body part. 

Hap­tic sen­sors can also be use­ful in every­day life and enhance exist­ing sys­tems. “Lifts, for exam­ple, usu­al­ly have a motion sen­sor that pre­vents the doors from clos­ing. But these sen­sors are pho­to­sen­si­tive, so they stop work­ing if the light is bro­ken,” explains Kostas Danas, “or if they are bad­ly placed, espe­cial­ly in rela­tion to the size of chil­dren. One could then imag­ine hap­tic sen­sors that block the door if they sense an obstacle.”

The hap­tic mate­r­i­al there­fore has many pos­si­ble appli­ca­tions as a hap­tic sen­sor, but these appli­ca­tions are not lim­it­ed to it. “There is already a com­pa­ny that uses these mate­ri­als to cre­ate micro-robots that deliv­er med­i­cines local­ly to the body. As these mate­ri­als are acces­si­ble with a mag­net, they can be guid­ed from the out­side. They could be moved through flu­ids, which are oth­er­wise com­pli­cat­ed to pass through.”

How­ev­er, the main appli­ca­tions of this new mate­r­i­al are prob­a­bly yet to be dis­cov­ered, as Kostas Danas pre­dicts, “appli­ca­tions are emerg­ing as dif­fer­ent peo­ple in indus­try or start-ups become inter­est­ed.” The researcher was award­ed a grant from the Euro­pean Research Coun­cil this year to devel­op an appli­ca­tion path for the hap­tic material.

Gaia Jouanna