Chapter a real world environment without any

Chapter 1                    


1.1      Robots

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A robot is defined as ” a machine that senses, thinks and
acts” 1.
For the sensing part the robot uses sensors to read the variables and
information of the robot’s environment. To process these information, the robot
needs onboard intelligence to make it capable of making decision about the environment.
Then, the robot needs some kind of actuator to perform the required action upon
the environment 1.

The need for robots

The need for robots has increased in the last century due to
the huge development in all different kinds industries, and the specific
requirement of the high-tech industries where a very high accuracy is needed. Robots
provide many characteristic that make using them is very desirable in many
industries and other fields:

Improving work efficiency  and productivity.

Providing high accuracy and

Increase the level of
safety, by replacing human workers in dangerous area.

The ability to use robots
in remote or undiscovered area.

The ability of doing routine
procedures and dull works that don’t attract human workers.


 Autonomy means that
the robot can operate in a real world environment without any external control
for a long period of time. Thus an Autonomous Robot is a machine that senses
it’s environment, and intelligently make decision about the action without any
help or control from a human processor 1.


Robots classification

Robots can be classified according to their wide variety in
shapes, applications, intelligence, degrees of autonomy and mobility. Two large
categories are, the industrial manipulator arms and the mobile robot, will be
discussed in this section.       Industrial manipulator

Manipulator arms, sometimes called robotic arms, consist of
links and joints that allow the relative motion between those links to perform
an action. A manipulator arm is shown in Figure 1.1.

Figure ?1.1 manipulator arm 2


Usually robotic arms are used in industrial fields to
perform the work that needs to be repeated in a high frequency, or the work
that may affect the humans health and safety such as working in dangerous or
dirty places. The robotic arms have many application such as welding, painting,
transportation of materials, assembly of machines and circuit boards, and
inspection in dangerous places. The end-effector  is the tool that the arm uses to  interact with the environment, such as the
welding tool in a welding robots or a grippers in the robots that  transfer materials 3.

Beside all the useful industrial application of the
manipulator arm it suffers from one major disadvantage;  the lack of mobility, which limits the
possible motions it can perform 3.       Mobile robots

Mobile robots are able to move within their environment
using legs, wheels or any other locomotion mechanism. Mobile robots are used in
dangerous and inhospitable environments, such as space or underwater. Figure
1.2 shows a mobile robot called Mars Pathfinder created by NASA and was sent to
Mars in 1997. Also many mobile robots are used within human environment to
perform tasks with a degree of autonomy.  Eufy Robot Vacuum RoboVac 11
shown in Figure  1.3, is a commercial
autonomous robotic vacuum cleaner. 






?Figure 1.2
Mars PathFinder 4







?Figure 1.3 Eufy
Robot  Vacuum RoboVac 11 5


There are increasing uses for mobile robots in those fields 6

Inspection of power lines
in smart grids.

Disaster recovery.

Military applications.

World Health Organizations.

Interaction with customers.


1.2      Mobile robots and locomotion

background information in this section are cited from  7 unless stated otherwise.

Mobile robots need a locomotion mechanism to move from a
place to another. There are many locomotion mechanism for robots such as
hopping, walking, rolling, running, crawling, swimming, sliding, skating and
flying. Figure 1.4 shows a swimming robot that is used to study damage at
Japan’s Fukushima nuclear plant.

 Most of those motion
mechanism are inspired by biological mechanisms. Biological systems have been
successful and efficient in harsh environments, and this make copying the
selection of the motion mechanism a useful thing.

However, there are some limitation for biological inspired
locomotion styles. For example, legged locomotion has more degrees of freedom
than wheels, thus it has more mechanical complexity. Also legged mechanisms
require more power than wheeled mechanisms on flat surfaces, while the legged
is more efficient on soft ground.


Figure ?1.4 Swimming robot to study damage at Japan’s Fukushima nuclear
plant 8


There are three issues that locomotion have, and affect
kinematics and dynamics probabilities of the robot:  

1.      Stability .

Characteristics of contact; including contact point/path, size and
shape angle of contact and friction.

3.      Type of environment;
including its structure and medium.


1.3      Classifications of mobile robots

Mobile robots can be classified according to the motion
system or the type of mobility. As shown in Table 1-1 the motion system can be ball
(Table 1-1(D)), legs (Table 1-1(E))  standard,
castor or Swedish  wheels (Table
1-1(A,B,C)). The types of motion either an omnidirectional  (Table 1-1(B,C,D,E) ) or not omnidirectional  (Table 1-1(A)). Omnidirectional means having
the ability to move at any direction in x-y plane from any orientation.

Motion System Based on




standard wheels

Castor wheel

Swedish wheels











Not omnidirectional


of mobility

Table ?1?1 Mobile robots classification. Adapted
from 6



 Legged robots

As mentioned before
wheeled robots are more efficient than legged robots on hard and smooth areas,
while  legged, shown in  Table 1-1(E), is more efficient on soft
ground. Also, its mentioned that the legged robots have more complicated
designs and mechanisms. In addition to complexity legged robots have velocity
limitations. Legged robots are omnidirectional means they can move at any
direction from any position. Furthermore, it can move at any kind of surfaces
and operates in very narrow spaces.





Wheeled robots

Wheeled robots are more common used kind due to: high
efficiency, design and model simplicity. As mentioned before there are two
types of wheels depending on the motion kind; omnidirectional and not
omnidirectional motion.       Not omnidirectional wheels

The robots that have not omnidirectional wheels have two
degrees of freedom and cannot perform homonymic motions such as sideway
movement. An example for such robots are shown in Table 1-1 (A).

 There is two types of
Standard wheel:

Fixed standard wheel that
doesn’t have the ability to rotate around its vertical axis and only limited to
move forward and  backward.

Steered standard wheel it
provides two degrees of freedom; rotation around the driven wheel axis and contact
point, also it can move forward and backward .       Omnidirectional wheels

Omnidirectional movement allows the robot to move at any
position regardless its orientation. Thus, omnidirectional robots have better maneuverability.
This movement can be performed with castor wheels in Table1-1(B) or Swedish
wheels in Table1-1(C).

Swedish wheels are consist of small rollers attached around
the circumference, this design let the wheel perform like a normal wheel, but
also the wheels rotation with very little friction along many possible
trajectories 7.       Number of wheels

The most common wheels number to be used in a mobile robot
are two, three or four wheels. Each choice has some advantages and
disadvantages 9:

Two wheels:

For static stability the minimum number of
wheels are two, and if the robot has a third point of contact with the ground two
wheeled robot can achieve  dynamic
stability too. The main advantage for the two wheels is the simple control, but
this design reduces the maneuverability.

Three wheels:

Three wheels are more stable than two
wheels, have more maneuverability and still simple to control.

Four wheels:

The static and dynamic stability for four
wheels robots are higher than two and three wheeled robots. Four wheeled robot
can achieve maneuverability, but has a relatively complex control.

1.4      Trajectory tracking and path following

Trajectory tracking is a design of control laws that  make the robot move from a point to another
following a defined path within a certain time (such as a circular path with
associated timing law). 10

Path following is a design of control laws that make the
robot converge to a certain path without time parameterization. 11

The path following controller can be used for spac problems