RobotSweater: Scalable, Generalizable, and Customizable
Machine-knitted Tactile Skins for Robots

RobotSweater is a machine-knitted pressure-sensitive low-cost tactile skin that is scalable, generalizable, and customizable. In this work, we design and fabricate a parameterized multi-layer tactile skin using off-the-shelf yarns with a programmable industrial knitting machine. We characterize our tactile skins to show their robust contact detection, multi-contact localization, and pressure sensing capability. Using our tactile skins, we demostrate closed-loop control with tactile feedback for human lead-through control of a robot arm and human-robot interaction with a mobile robot.

Paper link: https://arxiv.org/abs/2303.02858

Bibtex: 
@article{si2023robotsweater,
  title={RobotSweater: Scalable, Generalizable, and Customizable Machine-Knitted Tactile Skins for Robots},
  author={Si, Zilin and Yu, Tianhong Catherine and Morozov, Katrene and McCann, James and Yuan, Wenzhen},
  journal={arXiv preprint arXiv:2303.02858},
  year={2023}
}

Supplementary video

In this video, we present the sensor manufacturing procedure from sensor fabrication with a knitting machine to sensor assembly. We demonstrate the interaction between sensors and different objects along with visualization of sensor readings. In the end, we show two applications of RobotSweater sensors on a robot arm with human lead-through control and on a mobile robot with human-robot interaction.

Sensor design overview

An exploded view of the three-layer design: a perforated insulating mesh layer is sandwiched between two orthogonal layers of conductive stripes. The conductive stripes form a resistor matrix whose values change in response to applied pressure. Eyelets are placed along the borders for alignment and read-out purposes.

Sensor working principle

Left: Each intersection between the horizontal and vertical stripes can be modeled as a variable resistor. The resistance decreases as pressure increases.

Right: (a): the read-out board contains an Arduino nano, two multiplexers and a reference resistor; and it reads values of the resistor matrix.

(b): the schematic of the readout circuit. Due to the highly resistive yarn, row/column margin resistors of resistance ∼ 3KΩ are not negligible. Behaviors of taxel unit variable resistors are explained in the left figure.

Force sensitivity

Tactile readings of our sensors from each taxel unit, ricj (located at i-th row and j-th column), are linearly correlated to the gradually increased applied normal forces at different locations on (a) flat and (b) curved surfaces.

Repeatability

Repeatability test of our sensor. The experimental setup is shown on the bottom left. Using force-torque sensor’s z-axis readings as the ground truth load (black lines), we repeat force loading and unloading on a single taxel unit and plot the corresponding tactile reading (burgundy lines). We zoom in two cycles of: load, static contact, and unload at the beginning and the end of the test respectively.

Multi-contact detection and localization

Multi-contact detection as weights are placed at different locations. Taxel units are colored corresponding to the tactile readings, as shown in the bottom color bar. Notice the ghosting at r0c1 in the bottom right plot.

Acknowledgement

This research is supported by the CMU Manufacturing Futures Institute, made possible by the Richard King Mellon Foundation; and supported by the National Science Foundation under Award No. 1955444. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.