|We investigate the locomotion
of a surface-walking/climbing robot, the Planar Walker, based on a novel
planar eight-bar closed-loop mechanism. The robot can produce inchworm-like
movements in two orthogonal directions and can rotate about itself. The
locomotion mechanism to achieve such motions comprises four two-way linear
cylinders forming a deformable quadrilateral and four two-way gripper modules.
Decoupled transverse gaits and turning gaits of the robot with finite lengths
and finite rotation angles are obtained through the actuation of linear
cylinders and grippers. Actuation sequences of the cylinders and grippers
for different types of gaits are modeled using finite state machines. The
kinematics of the gaits are described using planar rigid motion group SE(2).
When a series of gaits are executed, the robot follows a non-smooth segmented
trajectory. Based on this feature, three point-to-point navigation methods
are developed for various scenarios: the Simple Line of Sight (SLS) algorithm,
the Simulated Annealing based Accurate Planning (SAAP) algorithm, and the
Localized Hybrid Accurate Planning (LHAP) algorithm. Computer simulation
shows that the SAAP algorithm produces accurate gait sequences and the LHAP
algorithm saves computation time and resources for long-range targets. However,
experimental results show that the inherent positional errors in individual
gait movements can be substantial when accumulated and can render a particular
algorithm less effective.