  Many teleoperation tasks require three or more tools working together, which
need the cooperation of multiple operators. The effectiveness of such schemes
may be limited by communication. Trimanipulation by a single operator using an
artificial third arm controlled together with their natural arms is a promising
solution to this issue. Foot-controlled interfaces have previously shown the
capability to be used for the continuous control of robot arms. However, the
use of such interfaces for controlling a supernumerary robotic limb (SRLs) in
coordination with the natural limbs, is not well understood. In this paper, a
teleoperation task imitating physically coupled hands in a virtual reality
scene was conducted with 14 subjects to evaluate human performance during
tri-manipulation. The participants were required to move three limbs together
in a coordinated way mimicking three arms holding a shared physical object. It
was found that after a short practice session, the three-hand tri-manipulation
using a single subject's hands and foot was still slower than dyad operation,
however, they displayed similar performance in success rate and higher motion
efficiency than two person's cooperation.
