(Schmidt and Berns, 2018). To perform the
requested tasks, climbing robots as all other
technical systems have to accomplish several
fulfilments which depend on the area of application.
However, commonly accepted requirements can be
figured applicable for practically all climbing robots
in the range of investigation and support:
a) Velocity and Mobility: The robot velocity and its
capability to move are two principal features in this
area. Based on the size of the piping construction it
might be obligatory to reach relatively high speed
even in vertical or horizontal direction. Furthermore,
it might be required to precisely manipulate and
position the system sidewards to investigate and
measure existing defects in the whole area of the
structure in 360
o
.
b) Payload: Based on the sensor type, locomotion,
as well as adhesion mechanisms, the vehicle needs
to be able to carry a payload of various weights.
c) Reliability and safety: Another significant non-
functional aspect is the robustness of the system. If
the tube-climbing robot fails during investigation
task, it would not be applicable in practice. Thus, the
reliability and safety requirements consist of robust
hardware, more advantageous controllers and
approaches to identify and take care of dangerous
situations and to rescue from them. Entirely, it might
be designated by rules to protect the robot within a
cable or wire to defeat the risk of a drop-off that
could hurt persons and destroy the system.
c) Reliability and Safety:
Another significant non-
functional aspect is the robustness of the system. If
the tube-climbing robot fails during the investigation
task, it would not be applicable in practice. Thus, the
reliability and safety requirements consist of
powerful hardware, more advantageous controllers
and approaches to identify and take care of
dangerous situations and to rescue from them.
Ultimately, it might be designated by rules to protect
the robot within a cable or wire to defeat the risk of
a drop-off that could hurt persons and destroy the
system.
d) Usability: Each of the abovementioned criteria is
significantly essential; however, this is only the
basis of the universal operability of the system. To
carry a vehicle system into operation, it has to be
more forceful, more efficient and less unsafe than
conventional methods, e.g., regarding inspection
systems. Moreover, it must be able to carry different
payloads (e.g., sensors or camera) depending on the
desired response, high mortality parts need to be
quickly replaceable, and the process must be faster
and less complicated compared to actual
technologies or methods.
By the performing task, a robot developer has to
determine which fulfilments have to be executed and
select applicable locomotion and adhesion
mechanisms.
2.3 Locomotion Types
a) Arms and Legs: The most general principle of
locomotion in the sphere of designing climbing
robots is the application of arms or legs. Based on
the specific type of task, climbing robots have been
constructed with the specified amount of limbs of
different degrees of freedom. The principal
advantage of this principle is high adaptability of a
robot to the surface structure. Every leg is designed
with adhesive components which allows an
examination of the foothold for the chosen attraction
forces. However, a significant amount of degrees of
freedom contributes to a complex mechanical
structure and control system. Also, this leads to
more considerable weight and greater torques.
Principally, the speed of these machines is
sufficiently low in consideration of other locomotion
mechanisms.
b) Wheels and Chains: For the operation on a
relatively smooth area, dozens of climbing robots
exist applying wheels or chain-driven locomotion. In
contrast to the legged systems, the adhesion and
locomotion components are decoupled in many
cases as used in different wheeled and tracked
machines. Another set of systems combine
locomotion and adhesion systems in the form of
electro adhesive or sticky tracks, tracks equipped
with suction cups or by magnetic wheels. The
significant advantage of wheeled or tracked
locomotion is the high speed, continuous movement
and the more straightforward mechanical design and
control elements. Nevertheless, these robots cannot
handle more substantial steps or obstacles, so they
are less adaptable to the surface characteristics and
are revealed to slip effects.
c) Sliding Frame: Particularly in combination with
pneumatic or magnetic adhesive systems sliding
frames are generally known. These principles
present a simple mechanical construction with two
frames which can move in a linear or rotational road