E-Skin Bimodal Sensors for Robotics and Prosthesis Using PDMS Molds Engraved by Laser

Abstract

Electronic skin (e-skin) is pursued as a key component in robotics and prosthesis to confer them sensing properties that mimic human skin. For pressure monitoring, a great emphasis on piezoresistive sensors was registered due to the simplicity of sensor design and readout mechanism. For higher sensitivity, films composing these sensors may be micro-structured, usually by expensive photolithography techniques or low-cost and low-customizable molds. Sensors commonly present different sensitivities in different pressure ranges, which should be avoided in robotics and prosthesis applications. The combination of pressure sensing and temperature is also relevant for the field and has room for improvement. This work proposes an alternative approach for film micro-structuration based on the production of highly customizable and low-cost molds through laser engraving. These bimodal e-skin piezoresistive and temperature sensors could achieve a stable sensitivity of −6.4 × 10−3 kPa−1 from 1.6 kPa to 100 kPa, with a very robust and reproducible performance over 27,500 cycles of objects grasping and releasing and an exceptionally high temperature coefficient of resistance (TCR) of 8.3%/°C. These results point toward the versatility and high benefit/cost ratio of the laser engraving technique to produce sensors with a suitable performance for robotics and functional prosthesis.

Flexible Sensors—From Materials to Applications

“…Providing robots with multiple sensory perceptions is a technological ambitious goal which aims to endow autonomous agents with the ability to better interact and cooperate within the dynamic human environment [609][610][611]. In Figure 16c,e artificial skins are foreseen as a potential opportunity to provide robots with sensory perceptions and biomimetic properties [612,613]. In this regard, various e-skins were produced which performed individual sensing such as skins capable of temperature sensing [441], motion tracking [372], and multi-modal skins capable of performing simultaneously pressure sensing and motion tracking [371].…”

Transduction Mechanisms, Micro-Structuring Techniques, and Applications of Electronic Skin Pressure Sensors: A Review of Recent Advances

“… Production of molds through laser engraving technique . This is a quite recent strategy to avoid the high costs of common photolithography processes without losing the high customization degree of the micro-structuring design as it happens with the use of unconventional molds, presenting, therefore, a high benefit/cost ratio [ 22 , 109 , 247 , 248 , 249 ]. Essentially, the laser beam transfers a high amount of energy that induces the melting or degradation of a material, creating cavities whose shape can be controlled through the design imported to the equipment, laser power and speed, as well as the material itself [ 22 , 247 ].…”

“…This is a quite recent strategy to avoid the high costs of common photolithography processes without losing the high customization degree of the micro-structuring design as it happens with the use of unconventional molds, presenting, therefore, a high benefit/cost ratio [ 22 , 109 , 247 , 248 , 249 ]. Essentially, the laser beam transfers a high amount of energy that induces the melting or degradation of a material, creating cavities whose shape can be controlled through the design imported to the equipment, laser power and speed, as well as the material itself [ 22 , 247 ]. The material with the cavities pattern can be posteriorly employed as a mold for soft lithography processes, commonly for micro-structuring PDMS [ 22 , 37 , 40 , 247 , 248 , 249 , 250 , 251 , 252 , 253 ] or PDMS composites [ 109 ].…”

“…Essentially, the laser beam transfers a high amount of energy that induces the melting or degradation of a material, creating cavities whose shape can be controlled through the design imported to the equipment, laser power and speed, as well as the material itself [ 22 , 247 ]. The material with the cavities pattern can be posteriorly employed as a mold for soft lithography processes, commonly for micro-structuring PDMS [ 22 , 37 , 40 , 247 , 248 , 249 , 250 , 251 , 252 , 253 ] or PDMS composites [ 109 ]. For piezoresistive sensors, these films have then been coated with carbon ink (by spin-coating) [ 22 , 247 , 248 , 249 ], CNTs (by drop-casting) [ 37 , 250 ], silver nanowires (by spin-coating) [ 252 ], or rGO (by spray-coating) [ 253 ] to become functional.…”

Synergistic Resistance Modulation toward Ultrahighly Sensitive Piezoresistive Pressure Sensors

“…In recent years, with the rapid development of prosthesis, [ 1,2 ] health monitoring, [ 3–7 ] and robot, [ 8–10 ] electronic skin has drawn huge research enthusiasm. Tactile sensation is one of the most significant functions of electronic skin, which mainly relies on pressure sensor to realize.…”