Direct Ink Write Strain Sensors for Continuum Robotics

Moyer, Daniel

Etd

Direct Ink Write Strain Sensors for Continuum Robotics

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The growing field of soft and continuum robotics requires new types of strain sensors that are stretchable, flexible, and can function at much higher strains than traditional strain gauges can handle. Sensors made of three different stretchable conductive materials (silver-polymer composite, carbon-polymer composite, and liquid metal composite) were printed using direct ink write onto stretchable thermoplastic polyurethane films. The response of the sensors was evaluated over a period of cyclic stretching under different strain, speed, and dwell conditions, and evaluated in terms of gauge factor, linearity, and drift. The results show that the silver-based sensor material has high drift, a gauge factor of between 1.75 and 21.06, and a linearity of between 82.4% and 99.63%. The carbon-based material has a slightly negative drift, a linearity of between 96.71% and 98.51%, and a gauge factor of between 1.65 and 3.69. The liquid metal-based material has low drift, a linearity of 99.8%, and a gauge factor of between 0.75 and 1.03. Based on these results, the printed liquid metal-based sensor was chosen for integration with two continuum robots, namely a 3D-printed concentric agonist-antagonist robot (CAAR) and a metal shape memory alloy notched wrist tube (NWT), by adhering the sensor onto the robot bodies. The printed liquid metal-based sensor showed good performance in tracking the motion of both types of robots. The endurance of the sensor for the CAAR was limited by the sensor detaching from the material due to the low temperature of lamination of the sensor onto the robot body, originating from the temperature limitation of the 3D printed CAAR material. The performance of the sensor for the NWT showed excellent motion tracking over the entire tested range. This work has shown that the sensor is easily manufacturable and that the digital design can be adjusted to fit a wide range of soft robots. The understanding of the behavior of the sensor over a range of conditions and an extended period of use allows a soft robot’s movement to be accurately tracked by the printed strain sensor.

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