A robotic surgical tool includes an elongate shaft having a working end
and a shaft axis, and a pair of linking arms each having a proximal end
and a distal end. The proximal end is pivotally mounted on the working
end of the shaft to rotate around a first pitch axis to produce rotation
in first pitch. A wrist member has a proximal portion pivotally connected
to the distal end of the linking arm to rotate around a second pitch axis
to produce rotation in second pitch. An end effector is pivotally mounted
on a distal portion of the wrist member to rotate around a wrist axis of
the wrist member to produce rotation in distal roll. The wrist axis
extends between the proximal portion and the distal portion of the wrist
member. The elongate shaft is rotatable around the shaft axis to produce
rotation in proximal roll. At about 90.degree. pitch, the wrist axis is
generally perpendicular to the shaft axis. The proximal roll around the
shaft axis and the distal roll around the wrist axis do not overlap. The
use of the linking arms allows the end effector to be bent back beyond
90.degree. pitch. The ability to operate the end effector at about
90.degree. pitch and to bend back the end effector renders the wrist
mechanism more versatile and adaptable to accessing hard to reach
locations, particularly with small entry points such as those involving
spinal, neural, or rectal surgical sites.