Integrated soft sensors and elastomeric actuators for tactile machines with kinesthetic sense

Abstract

Human skin contains highly specialized deformation receptors that allow us to intuitively and effortlessly interpret our surroundings. These sensors help us to localize touch and determine the degree of contact pressure. In addition, the innate understanding of our own body posture is also due to these mechanoreceptors. This work demonstrates a synthetic sensory-motor analog that can be 3D printed, using direct ink writing (DIW) onto soft, fluidic elastomer actuators (FEAs). This 3D printing technique uses two inks-one that is an ionically conductive hydrogel and another that is an electrically insulating silicone-which is then patterned and photopolymerized into stretchable capacitive sensors. In this paper, these sensors are used to enable tactile sensing and kinesthetic feedback in a pneumatically actuated haptic device. This capacitive skin enabled the device to detect a compressive force from a finger press of ~2 N, and an internal pressurization of as low as ~ 10 kPa.

Flaw sensitivity of highly stretchable materials

“…Under development are new fields of applications, including tissue regeneration [1], drug delivery [2], artificial muscles [3][4][5], stretchable electronics [5][6][7][8][9], and soft robots [10,11]. Stretchable, transparent, ionic conductors (e.g., hydrogels and ionogels) enable devices of unusual functions, such as transparent loudspeakers [12], artificial skins [13], artificial axons [14,15], and electroluminescence of giant stretchability [16][17][18]. The interest in the mechanics of stretchable materials has surged [19][20][21][22][23][24][25][26][27][28][29][30][31][32].…”

Meet the soft, cuddly robots of the future

“…You can tune them to respond to a slight brush of a finger or to a 30-pound weight, " says mechanical engineer Robert Shepherd at Cornell, who has developed methods for 3D printing stretch-sensitive 'skins' directly onto soft robots 10 . Alternating layers of conductive and insulating material produce an electrical signal when prodded or pulled.…”

Dielectric Elastomer Sensors

“…Ionic conductors have been studied for use in applications that demand greater stretch and greater transparency than electronic conductors, such as polyacrylamide hydrogels [56][57][58] and ionogels composed of ionic liquid and polyacrylic acid [59]. Recent work has demonstrated that these materials can be used as the electrodes of transparent sensors and actuators for artificial muscles, skin, axons and kinesthetic sensing [60][61][62][63][64]. A transparent, capacitive sensor termed ionic skin was first developed using a dielectric elastomer covered with ionic electrodes, which were composed of a polyacrylamide hydrogel with NaCl [9].…”

“…Ionic conductors have attracted attention in capacitive tactile sensing applications, due to their high transparency and conductivity under large deformation [61][62][63]. Nie et al [61] fabricated a capacitive pressure sensor utilizing an ionic gel matrix.…”

“…The results of tests using this device showed that the sensor could detect tissue elasticity from 0.1 to 0.5 MPa. Dielectric elastomer sensors have also been used as self-sensing actuators, such as pneumatic actuators [62], dielectric elastomer actuators [87], coaxial actuators [88] and McKibben actuators [39].…”