Instrumentation & Measurement Magazine 26-2 - 49

Fig. 1. Gecko shape and structure diagram of gecko robot: (a) Bionic object: gecko. (b) Gecko-mimicking robot design. (c) Force sensor and signal transmission board.
gecko-mimicking robot limbs in stable climbing on vertical
surfaces was proposed.
The above research shows that all kinds of robots working
on the vertical surfaces have matching application scenarios.
Among them, the gecko-mimicking robot that adopts the
dry adhesion method has more flexible movement ability and
obstacle-crossing performance, and the robot machine consumes
less energy. It is the best choice for maintenance tasks
on smooth metal and glass surfaces in the vertical direction. To
solve the problem of instability and falling of the dry-adhesion
robot on the vertical arc surface, the limb mechanics regulation
strategy will be studied when the swinging phase limb is disengaged,
and the influence of the compliance force control on
the stability of the body of the robot will be analyzed. Through
the main kinetic regulation of the foot, the stability of the imitation
gecko robot's climbing movement on the vertical arc
surface will be added.
Mechanical Regulation Strategy of
the Arc Surface Limbs of the Geckomimicking
Robot
The gait control of wall-climbing robots is similar to the
limbed robots, where the foot end motion is divided into
the swing phase and the stance phase; however, there is
a significant difference in the state of force during movement.
When the swinging phase leaves the arc surface,
there is transformation of the robot foot end from an adhesion
state to a detachment state. The body of the robot will
be disturbed by the external force which caused by the motion
inertia force or the adhesion force, and the disturbance
force will be transmitted to the stance phase limbs under
the closed chain system. Accordingly, the force of the stance
phase limbs in the process of the movement will be analyzed
and the corresponding mechanical control algorithm will be
designed to improve the stability of the robot in the process
of the climbing. The right front limb is used as the swing
phase limb to walk on a single step to give a schematic
April 2023
diagram of the camber movement. The whole process is the
coordination and alternation of multiple feet to realize camber
climbing.
Robot Platform
In this study, a novel wall-climbing robot equipped with foot
end 3D force sensors is introduced. In previous work, we realized
that both the robot mass and the position of the mass
center could affect the wall-climbing stability; thus a geckoscale,
light-weight robot structure is redesigned. The detailed
scale parameters are shown in Fig. 1. Dynamixel XL330 is
adopted as the robot actuator, communicating with main controller
Raspberry Pi 4 via half duplex UART. A 1300-mAh Li-Po
battery is attached, providing the whole system power. As for
the adhesion feet, the passive adhesion feet were adopted,
which is different from the gecko's toes. The main reason for
the gecko toe inward rolling is the active elimination of the inter-foot
tangential force on the lock. Because the lock effect of
this robot is mainly reflected in the inter-foot normal force on
the lock, the force can rely on the limb to apply force to eliminate
it, so the robot no longer needs to have an additional
outward rolling mechanism for detachment. More importantly,
four small-scale 3D force sensors [14] are combined with
the robot limbs, with which the force acquisition can run at 1
KHz on Raspberry Pi 4 via CAN.
Limb Compliant Motion Control Algorithm
To reduce the contact force between the swing phase limb and
the environment, a compliant motion control algorithm for
the limbs of the stance phase is designed to reduce the impact
of the external force on the closed-chain system. The compliant
motion controller requires simple, efficient and adjustable
parameters. Admittance control is the most effective mechanical
regulation algorithm. The three-dimensional force sensor
on the robot foot is used to measure the relationship between
the foot force and the desired force in the current state to adjust
the motion trajectory of the foot which is used to realize the
IEEE Instrumentation & Measurement Magazine
49

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