comp322/s2000/l31 components of a robotic system robot: articulated mechanical system with actuators...
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COMP322/S2000/L3 1
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
COMP322/S2000/L3 2
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
COMP322/S2000/L3 3
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
COMP322/S2000/L3 4
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.
COMP322/S2000/L3 5
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.
COMP322/S2000/L3 6
Classification of Robot Arms: by Drive Technology
Hydraulic Power Supply
Pneumatic Power Supply
COMP322/S2000/L3 7
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
COMP322/S2000/L3 8
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
COMP322/S2000/L3 9
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
COMP322/S2000/L3 10
Examples of Cartesian Robots
COMP322/S2000/L3 11
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
COMP322/S2000/L3 12
Example of Cylindrical Robots
COMP322/S2000/L3 13
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
COMP322/S2000/L3 14
Example of Spherical Robots
COMP322/S2000/L3 15
Examples of Spherical Robots and the work envelope
Range of motion of the 5 axes
GeneralView
Working Volume
COMP322/S2000/L3 16
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
COMP322/S2000/L3 17
Example of SCARA Robots
COMP322/S2000/L3 18
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
COMP322/S2000/L3 19
Example of Articulated Robots
COMP322/S2000/L3 20
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)