Manipulator Mechanism Design

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Manipulator Mechanism Design

• Contents of lecture
• Design of robot cells.
• Manipulator mechanism design
• Selection of Manipulators

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A Robot Cell

• Robot arm
• (manipulator)

Tool
Fence
Fixture
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A Robot System
Additional equipment
Fixtures
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Selecting a Manipulator
Typical price 25 of total robot system
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Task Dependent requirements

• Workspace
• Must reach a number of fixtures and workpieces
• Air around fixtures and workpieces in order to
  avoid collisions
• Consider the shape and singularities
• Load capacity
• Speed
• Repeatability and accuracy

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Degrees of Freedom (DOF)

• General positioning and orienting requires 6
  degrees of freedom (DOF).
• Tasks with with symmetric tool requires only 5
  DOF (welding, grinding, polishing etc.)

• Positioning parts on planar surface (pick and
  place) requires only 4 DOF (X,Y,Z and ?).

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Degrees of Freedom (DOF)

• Application of external tilt/roll manipulators
  may be required due to process requirements
  (welding)

• Externally applied DOFs counts in the system.
  I.e. symmetric tool and 2 External DOFs leaves
  only a requirement for 3 DOFs in the robot.
• Symmetric parts may reduce the number of required
  DOFs.

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Kinematic configuration

• Number of joints equals number of DOFs for serial
  kinematic linkages.
• Positioning structure and orienting
  structure/wrist.
• Classification according to first 3 joints
  (positioning structure)

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Kinematic configuration
Articulated (RRR)

• Two shoulder joints (vertical horizontal
  elevation) and an elbow joint parallel to the
  elevation joint.
• Provides the least intrusion of the manipulator
  structure into the workspace.

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Kinematic configuration
Cartesian (TTT)

• Stiff structures allow construction of large
  robots, often referred to as gantry robots.
• Does not produce kinematic singularities for
  first 3 axes.
• All feeders, fixtures and other equipment must be
  placed inside the robot

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Kinematic configuration
Scara (RRT)

• Three revolute parallel joints allowing it to
  move and orient in plane.
• First three joints dont support weight of
  manipulator/tool/workpiece.
• Usually very fast robots.
• Well suited to pick and place.

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Kinematic configuration
Spherical (RRT)

• Much like articulated robot, except that joint 3
  is prismatic.
• More suitable than articulated robot for some
  applications (entering narrow holes).

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Kinematic configuration
Cylindrical

• Much like spherical robots, except that joint 2
  is prismatic.
• More suitable to some applications than
  articulated and spherical robots.

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Kinematic configuration
Closed structures

• Increased stiffness
• Reduced allowable range of motion

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Exercise
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Skitse af bukkecelle I
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Skitse af bukkecelle II