In science fiction robots are already human’s best friend but in reality we will only see robots for specific jobs as universal programmable machine slave in the near future which leads to interesting questions,
What is a Robot?
Robots are physical agents that perform tasks by manipulating the physical world. They are equipped withsensors to perceive their environment and effectors to assert physical forces on it. Robots can be put into three main categories: manipulators, mobile
robots and humanoid robots.
Robotics and AI
Artificial intelligence is a theory. The base object is the agent who is the "actor". It is realized in software.
Robots are manufactured as hardware. The connection between those two is that the control of the robot is
a software agent that reads data from the sensors, decides what to do next and then directs the effectors to
act in the physical world.
Robots are manufactured as hardware. The connection between those two is that the control of the robot is
a software agent that reads data from the sensors, decides what to do next and then directs the effectors to
act in the physical world.
-Theory and Application
- Robot Hardware
--Sensors
Sensors are the perceptual interface between robots and
their environment. 1 On the one hand we have passive sensors
like cameras, which capture signals that are generated
by other sources in the environment. On the other hand we
have active sensors (for example sonar, radar, laser) which
emit energy into the environment. This energy is reflected
by objects in the environment. These reflections can then
be used to gather the information needed.
Generally active sensors provide more information than passive
sensors. But they also consume more power. This can
lead to a problem on mobile robots which need to take their
energy with them in batteries.
We have three types of sensors (no matter whether sensors
are active or passive). These are sensors that either
² record distances to objects or
² generate an entire image of the environment or
² measure a property of the robot itself.
Many mobile robots make use of range finders, which measure distance to nearby objects. A common
type is the sonar sensor. Alternatives to sonar include radar and laser .Some range sensors measure very short or very long distances. Close-range sensors are often tactile sensors
such as whiskers, bump panels and touch-sensitive skin. The other extreme are long-range sensors like the
Global Positioning SystemThe second important class of sensors are imaging sensors. These are cameras that provide images of
the environment that can then be analyzed using computer vision and image recognition techniques.
The third important class are proprioceptive sensors. These inform the robot of its own state. To
measure the exact configuration of a robotic joint motors are often equipped with shaft decoders that count
the revolution of motors in small increments. Another way of measuring the state of the robot is to use
force and torque sensors. These are especially needed when the robot handles fragile objects or objects
whose exact shape and location is unknown. Imagine a ton robot manipulator screwing in a light bulb.
their environment. 1 On the one hand we have passive sensors
like cameras, which capture signals that are generated
by other sources in the environment. On the other hand we
have active sensors (for example sonar, radar, laser) which
emit energy into the environment. This energy is reflected
by objects in the environment. These reflections can then
be used to gather the information needed.
Generally active sensors provide more information than passive
sensors. But they also consume more power. This can
lead to a problem on mobile robots which need to take their
energy with them in batteries.
We have three types of sensors (no matter whether sensors
are active or passive). These are sensors that either
² record distances to objects or
² generate an entire image of the environment or
² measure a property of the robot itself.
Many mobile robots make use of range finders, which measure distance to nearby objects. A common
type is the sonar sensor. Alternatives to sonar include radar and laser .Some range sensors measure very short or very long distances. Close-range sensors are often tactile sensors
such as whiskers, bump panels and touch-sensitive skin. The other extreme are long-range sensors like the
Global Positioning SystemThe second important class of sensors are imaging sensors. These are cameras that provide images of
the environment that can then be analyzed using computer vision and image recognition techniques.
The third important class are proprioceptive sensors. These inform the robot of its own state. To
measure the exact configuration of a robotic joint motors are often equipped with shaft decoders that count
the revolution of motors in small increments. Another way of measuring the state of the robot is to use
force and torque sensors. These are especially needed when the robot handles fragile objects or objects
whose exact shape and location is unknown. Imagine a ton robot manipulator screwing in a light bulb.
Effectors
Effectors are the means by which robots manipulate the environment, move and change the shape of their
bodies.
To understand the ability of a robot to interact with the physical world we will use the abstract concept of
a degree of freedom (DOF). We count one degree of freedom for each independent direction in which a
robot, or one of its effectors can move. As an example lets contemplate a rigid robot like an autonomous
underwater vehicle (AUV). It has six degrees of freedom, three for its (x;y; z) location in space and three
for its angular orientation (also known as yaw, roll and pitch). These DOFs define the kinematic state of
the robot. This can be extended with another dimension that gives the rate of change of each kinematic
dimension. This is called dynamic state.
Robots with nonrigid bodies may have additional DOFs. For example a human wrist has three degrees
of freedom – it can move up and down, side to side and can also rotate. Robot joints have 1, 2, or 3 degrees
of freedom each. . Revolute joints generate rotational motion
while the prismatic joints generates sliding motion.
If you take your arm as an example you will notice, that it
has more than six degrees of freedom. If you put your hand
on the table you still have the freedom to rotate your elbow.
Manipulators which have more degrees of freedom than required
to place an end effector to a target location are easier
to control than robots having only the minimum number of DOFs.
Mobile robots are somewhat special. The number of degrees of freedom do not need to have corresponding
actuated elements. Think of a car. It can move forward or backward, and it can turn, giving it two
DOFs. But if you describe the car’s kinematic configuration you will notice that it is three-dimensional.
On a flat surface like a parking site you can maneuver your car to any (x;y) point, in any orientation. You
see that the car has 3 effective DOFs but only 2 controllable DOFs. We say a robot is nonholonomic if it
has more effective DOFs than controllable DOFs and holonomic if the two numbers are the same.
Holonomic robots are easier to control than nonholonomic (think of parking a car: it would be much easier
to be able to move the car sideways). But holonomic robots are mechanically more complex. Most
manipulators and robot arms are holonomic and most mobile robots are nonholonomic.
bodies.
To understand the ability of a robot to interact with the physical world we will use the abstract concept of
a degree of freedom (DOF). We count one degree of freedom for each independent direction in which a
robot, or one of its effectors can move. As an example lets contemplate a rigid robot like an autonomous
underwater vehicle (AUV). It has six degrees of freedom, three for its (x;y; z) location in space and three
for its angular orientation (also known as yaw, roll and pitch). These DOFs define the kinematic state of
the robot. This can be extended with another dimension that gives the rate of change of each kinematic
dimension. This is called dynamic state.
Robots with nonrigid bodies may have additional DOFs. For example a human wrist has three degrees
of freedom – it can move up and down, side to side and can also rotate. Robot joints have 1, 2, or 3 degrees
of freedom each. . Revolute joints generate rotational motion
while the prismatic joints generates sliding motion.
If you take your arm as an example you will notice, that it
has more than six degrees of freedom. If you put your hand
on the table you still have the freedom to rotate your elbow.
Manipulators which have more degrees of freedom than required
to place an end effector to a target location are easier
to control than robots having only the minimum number of DOFs.
Mobile robots are somewhat special. The number of degrees of freedom do not need to have corresponding
actuated elements. Think of a car. It can move forward or backward, and it can turn, giving it two
DOFs. But if you describe the car’s kinematic configuration you will notice that it is three-dimensional.
On a flat surface like a parking site you can maneuver your car to any (x;y) point, in any orientation. You
see that the car has 3 effective DOFs but only 2 controllable DOFs. We say a robot is nonholonomic if it
has more effective DOFs than controllable DOFs and holonomic if the two numbers are the same.
Holonomic robots are easier to control than nonholonomic (think of parking a car: it would be much easier
to be able to move the car sideways). But holonomic robots are mechanically more complex. Most
manipulators and robot arms are holonomic and most mobile robots are nonholonomic.
Movement
For mobile robots a special group of effectors are the mechanisms the robot uses for locomotion, including
wheels, tracks, and legs. The differential drive consists of two independently actuated wheels – one on
each side. If both wheels move at the same velocity, the robot moves on a straight line2. If they move in
opposite directions, the robot turns on the spot.
An alternative is the synchro drive3, in which each wheel can move and turn around its own axis. This could
easily lead to chaos. But if you assure the constraint that all wheels always point in the same direction and
move with the same speed your robot is save.If you have ever tried to implement that (for example with a Lego Mindstorm) you know this can become hard especially with
cheap hardware,
Both differential and synchro drives are nonholonomic. Some more expensive robots use holonomic drives,wheels, tracks, and legs. The differential drive consists of two independently actuated wheels – one on
each side. If both wheels move at the same velocity, the robot moves on a straight line2. If they move in
opposite directions, the robot turns on the spot.
An alternative is the synchro drive3, in which each wheel can move and turn around its own axis. This could
easily lead to chaos. But if you assure the constraint that all wheels always point in the same direction and
move with the same speed your robot is save.If you have ever tried to implement that (for example with a Lego Mindstorm) you know this can become hard especially with
cheap hardware,
which usually involve three or more wheels and can be oriented and moved independently.
Power Sources
Robots need a power source to drive their effectors. The most popular mechanism for both manipulator
actuation and locomotion is the electric motor.
Other possible ways are pneumatic actuation using compressed gas and hydraulic actuation using pressurized
fluids. They have their application niches but are not widely used.
actuation and locomotion is the electric motor.
Other possible ways are pneumatic actuation using compressed gas and hydraulic actuation using pressurized
fluids. They have their application niches but are not widely used.
Bits and Pieces
Most robots have some kind of digital communication like wireless networks. Especially today those
modules get cheaper. They can be used for communication between robots or for some kind of back link
to the robots home station.
modules get cheaper. They can be used for communication between robots or for some kind of back link
to the robots home station.
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