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Components of a Robotic System

Robot:ArticulatedMechanical

Systemwith Actuators

Computer

TaskEnvironment

Interaction

Control

Language(Program)

Internal “sensed”Information

e.g. force

External “sensed”Information

e.g. camera, sonar

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Components of a Robotic System

• Robotic System is Task specific• Sensory information (internal and External) provides

intelligence to the system but generates many challenging research topics

• The Mechanical System with Actuators INTERACT with the Environment

• The Computer System CONTROLS the Robot

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Classification of Robot Arms: by Drive Technology

• Hydraulic System– made up of an electric motor that pumps a non-compressible

fluid into a system consisting of a reserve tank, control valves and actuators to transmit energy.

– generally associated with larger robots– Advantages:

• greater power, i.e. can handle heavy load• greater speed

– Disadvantages:• occupies large floor space• tendency to leak oil => dirty• noisy

– Applications: for heavy “dirty” task, e.g. welding in automobile and aircraft industries

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Classification of Robot Arms: by Drive Technology

• Hydraulic System• Electric System

– AC motor, DC servo or stepper motor– for small robots– Advantages:

• high accuracy• high repeatability• clean

– Disadvantages:• less power, i.e. less payload• slower

– Applications: assembly tasks that requires precision, e.g. circuit board.

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Classification of Robot Arms: by Drive Technology

• Hydraulic System• Electric System• Pneumatic System

– Uses compressed air– for smaller robots with fewer degrees of freedom– Advantages:

• readily installed since compressed air is readily available in factory floors and laboratories

– Disadvantages:• difficult to provide good precision due to the fact that air is

compressible , easily affected by temp., humidity, etc.

– Applications:control of grippers to provide compliance in grasping objects, e.g. SONY robots in the lab.

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Classification of Robot Arms: by Drive Technology

Hydraulic Power Supply

Pneumatic Power Supply

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Classification of Robot Arms:Work Envelope Geometry

Kinematics of Robot Arms is defined as the Relationship between arm (link) parameters and the configuration (position and orientation) of the end-effector with respect to a reference point

Arm parameters: motion of joints• Prismatic (P) - Linear motion ALONG an axis• Revolute (R) - Rotary motion ABOUT an axis

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Classification of Robot Arms:by Work Envelope Geometry

Definition: The Gross Work Envelope of a robot is defined as the LOCUS of points in the 3D space that can be reached by the “wrist” (end effector).

Considering 3 major axes only: (5 types)

Axis 1 Axis 2 Axis 3

Cartesian P P P

Cylindrical R P P

Spherical R R P

SCARA R R P

Articulated R R R

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Cartesian

• Rectangular-coordinates Robot

• 3 linear axes (P,P,P)

Advantages:– Easy to visualize

– Rigid structure

– Easy to program off-line

– Good repeatability and accuracy

Disadvantages:– Requires large floor space for the

large structure

– Can only reach in front of itself

– Restriction on the compatibility with other types of arms in a common work space

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Examples of Cartesian Robots

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Cylindrical

• Work space is the space between 2 concentric cylinders of the same height

• 2 Prismatic (linear) axes (P,P) and 1 Rotational axis (R)

Advantages:– Rigid structure

– Easy to program off-line

– Good repeatability and accuracy

Disadvantages:– Horizontal motion is circular only

– Restriction on the compatibility with other types of arms in a common work space

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Example of Cylindrical Robots

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Spherical• Polar-coordinates Robot• 1 linear axis (P), 2 rotational axes (R)• Work envelope is the volume of

concentric spheres but truncated from above, below and behind (where the arm cannot reach)

Advantages:– can be light in weight– Easy to program – Good precision

Disadvantages:– Large and variable torques on joints 2,3

=> the counter balance problem– Positional error is proportional to the

radius at which the arm is operating

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Example of Spherical Robots

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Examples of Spherical Robots and the work envelope

Range of motion of the 5 axes

GeneralView

Working Volume

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SCARA

• Selected Compliance Assembly Robot Arm

• 1 linear axis (P) and 2 rotational (R) axes

• Work envelope similar to the cylindrical one

Advantages:– Relatively inexpensive

– Height axis is rigid => good for insertion type of tasks

– Good repeatability

Disadvantages:– Difficult to program off-line

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Example of SCARA Robots

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Articulated

• Closely resembles a human arm

• 3 rotational axes (R,R,R)

Advantages:– Most flexible

– Most anthropomorphic

– Compatible with other robots working in common work space

Disadvantages:– Most difficult to control

– Accuracy can be poor

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Example of Articulated Robots

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References

Diagrams and figures are from the following references:

• James L. Fuller, Robotics - Introduction, Programming, and Projects, Prentice Hall, 2nd edition, 1999. (ISBN: 0-13-095543-4)

• Robert J. Schilling, Fundamentals of Robotics - Analysis & Control, Prentice Hall, 1990. (ISBN: 0-13-344433-3)