  Force perception on medical instruments is critical for understanding the
mechanism between surgical tools and tissues for feeding back quantized force
information, which is essential for guidance and supervision in robotic
autonomous surgery. Especially for continuous curvilinear capsulorhexis (CCC),
it always lacks a force measuring method, providing a sensitive, accurate, and
multi-dimensional measurement to track the intraoperative force. Furthermore,
the decoupling matrix obtained from the calibration can decorrelate signals
with acceptable accuracy, however, this calculating method is not a strong way
for thoroughly decoupling under some sensitive measuring situations such as the
CCC. In this paper, a three-dimensional force perception method on
capsulorhexis forceps by installing Fiber Bragg Grating sensors (FBGs) on
prongs and a signal decoupling method combined with FASTICA is first proposed
to solve these problems. According to experimental results, the measuring range
is up to 1 N (depending on the range of wavelength shifts of sensors) and the
resolution on x, y, and z axial force is 0.5, 0.5, and 2 mN separately. To
minimize the coupling effects among sensors on measuring multi-axial forces, by
unitizing the particular parameter and scaling the corresponding vector in the
mixing matrix and recovered signals from FastICA, the signals from sensors can
be decorrelated and recovered with the errors on axial forces decreasing up to
50% least. The calibration and calculation can also be simplified with half the
parameters involved in the calculation. Experiments on thin sheets and in vitro
porcine eyes were performed, and it was found that the tearing forces were
stable and the time sequence of tearing forceps was stationary or first-order
difference stationary during roughly circular crack propagating.
