  In typical in-hand manipulation tasks represented by object pivoting, the
real-time perception of rotational slippage has been proven beneficial for
improving the dexterity and stability of robotic hands. An effective strategy
is to obtain the contact properties for measuring rotation angle through
visuotactile sensing. However, existing methods for rotation estimation did not
consider the impact of the incipient slip during the pivoting process, which
introduces measurement errors and makes it hard to determine the boundary
between stable contact and macro slip. This paper describes a generalized 2-d
contact model under pivoting, and proposes a rotation measurement method based
on the line-features in the stick region. The proposed method was applied to
the Tac3D vision-based tactile sensors using continuous marker patterns.
Experiments show that the rotation measurement system could achieve an average
static measurement error of 0.17 degree and an average dynamic measurement
error of 1.34 degree. Besides, the proposed method requires no training data
and can achieve real-time sensing during the in-hand object pivoting.
