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