  Tactile sensing is essential for robots to perceive and react to the
environment. However, it remains a challenge to make large-scale and flexible
tactile skins on robots. Industrial machine knitting provides solutions to
manufacture customizable fabrics. Along with functional yarns, it can produce
highly customizable circuits that can be made into tactile skins for robots. In
this work, we present RobotSweater, a machine-knitted pressure-sensitive
tactile skin that can be easily applied on robots. We design and fabricate a
parameterized multi-layer tactile skin using off-the-shelf yarns, and
characterize our sensor on both a flat testbed and a curved surface to show its
robust contact detection, multi-contact localization, and pressure sensing
capabilities. The sensor is fabricated using a well-established textile
manufacturing process with a programmable industrial knitting machine, which
makes it highly customizable and low-cost. The textile nature of the sensor
also makes it easily fit curved surfaces of different robots and have a
friendly appearance. Using our tactile skins, we conduct closed-loop control
with tactile feedback for two applications: (1) human lead-through control of a
robot arm, and (2) human-robot interaction with a mobile robot.
