Open-loop Printing of Liquid Metal for the Low-cost Rapid Fabrication of Soft Sensors

Soft sensors using a highly conductive liquid metal eGaIn(eutectic gallium-indium) are widely researched due to the increasing need for flexible sensors such as temperature sensors, haptic sensors, multi-modal sensors and force sensors. Manufacturing methods for these soft sensors have been explored including printing, injection, lithography and spraying. Among these methods, direct writing of eGaIn is the fastest and simplest method. Other methods are mostly conventional mold-based fabrication while printing does not require complicated pre-processing of elastomer. Although existing printing methods are able to pattern the liquid metal into various designs within micro scale, these methods either require high-precision feedback control over SOD, extrusion rate, low stage velocity or modification of liquid metal. As a result, the low tolerance in parameters of printing or extra modification of liquid metal make it difficult to replicate the work. Therefore, as a trade-off between printing quality and tolerance in precision, in this paper we present two open loop liquid metal printing methods with higher tolerance in precision using a low-cost open source system without the need to modify property of liquid metal. We discuss how parameters and setup of the printer will affect the printing quality. We also discuss how well the printing methods can resist variation in substrate height. As an example of applications of the proposed methods, we manufacture a strain sensor using the proposed method and demonstrate calibration result of the sensor. In general, these printing methods are alternative ways to manufacture liquid metal sensors when high accuracy is not desired