Abstract
The excellent compliance and large range of motion of soft actuators controlled by fluid pressure has lead to strong interest in applying devices of this type for biomimetic and human-robot interaction applications. However, in contrast to soft actuators fabricated from stretchable silicone materials, conventional technologies for position sensing are typically rigid or bulky and are not ideal for integration into soft robotic devices. Therefore, in order to facilitate the use of soft pneumatic actuators in applications where position sensing or closed loop control is required, a soft pneumatic bending actuator with an integrated carbon nanotube position sensor has been developed. The integrated carbon nanotube position sensor presented in this work is flexible and well suited to measuring the large displacements frequently encountered in soft robotics. The sensor is produced by a simple soft lithography process during the fabrication of the soft pneumatic actuator, with a greater than 30% resistance change between the relaxed state and the maximum displacement position. It is anticipated that integrated resistive position sensors using a similar design will be useful in a wide range of soft robotic systems.
Highlights
In soft robotics, the rigid structures of traditional “hard” robots are replaced with innovative, compliant designs fabricated using flexible materials
The carbon nanotube resistive sensor was produced by a simple soft lithography process using the laser-engraved acrylic mould and a 0.5% dispersion of multi-walled carbon nanotubes (MWCNT) in isopropanol (IPA) by weight
There is a substantial 38% decrease in sensor resistance between the relaxed and fully bent state, confirming that the integrated carbon nanotube large strain sensor is well suited to measuring the displacement of a soft pneumatic actuator
Summary
The rigid structures of traditional “hard” robots are replaced with innovative, compliant designs fabricated using flexible materials. PneuNets bending actuators use controlled inflation of moulded expandable chambers to achieve large bending displacements and are a flexible design well suited to varied soft robotics applications. Soft robots have much higher compliance, and even small applied forces can cause significant deformation This deformation is distributed across the entire flexible structure of the soft robot. For accurate control of soft robots, position sensing is both more necessary and more difficult Conventional rigid sensors, such as encoders and metal or silicon strain gauges, are ill suited to soft robotics applications [11]. The carbon nanotube resistive sensor is integrated during the fabrication of the soft bending actuator by a simple soft lithography process and is able to measure the position of the soft bending actuator over a displacement range of 270◦. In comparison to current state of the art sensors using liquid metals or conductive grease, this sensor has the advantages of easier integration in the fabrication process, a thin 0.3-mm thickness (avoiding stiffening of the actuator structure) and, due to the moulding process used for fabrication, is expected to be ideally suited for manufacturing sensors at multiple locations at one time
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