Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001

39.4.1 EOAT Design

 

· Typical factors to be considered are,

  1. Workpiece to be handled
    1. part dimensions
    2. mass
    3. pre- and post- processing geometry
    4. geometrical tolerances
    5. potential for part damage
  2. Actuators
    1. mechanical
    2. vacuum
    3. magnet
    4. etc.
  3. Power source of EOAT
    1. electrical
    2. pneumatic
    3. hydraulic
    4. mechanical
  4. Range of gripping force
    1. object mass
    2. friction or nested grip
    3. coefficient of friction between gripper and part
    4. maximum accelerations during motion
  5. Positioning
    1. gripper length
    2. robot accuracy and repeatability
    3. part tolerances
  6. Maintenance
    1. number of cycles required
    2. use of separate wear components
    3. design for maintainability
  7. Environment
    1. temperature
    2. humidity
    3. dirt, corrosives, etc.
  8. Temperature protection
    1. heat shields
    2. longer fingers
    3. separate cooling system
    4. heat resistant materials
  9. Materials
    1. strong, rigid, durable
    2. fatigue strength
    3. cost and ease of fabrication
    4. coefficient of friction
    5. suitable for environment
  10. Other points
    1. interchangeable fingers
    2. design standards
    3. use of mounting plate on robot
    4. gripper flexible enough to accommodate product design change

 

· The typical design criteria are,

  1. - low weight to allow larger payload, increase accelerations, decrease cycle time
  2. - minimum dimensions set by size of workpiece, and work area clearances
  3. - widest range of parts accommodated using inserts, and adjustable motions
  4. - rigidity to maintain robot accuracy and reduce vibrations
  5. - maximum force applied for safety, and to prevent damage to the work
  6. - power source should be readily available from the robot, or nearby
  7. - maintenance should be easy and fast
  8. - safety dictates that the work shouldn't drop when the power fails

 

 

· Other advanced design points,

  1. - ensure that part centroid is centered close to the robot to reduce inertial effects. Worst case make sure that it is between the points of contact.
  2.  
  1. - holding pressures/forces/etc are hard to control, try to hold parts with features or shapes
  2.  
  1. - compliance can help guide work into out-of-alignment conditions.
  2. - sensors in the EOAT can check for parts not in the gripper, etc.
  3. - the gripper should tolerate variance in work position with part alignment features
  4. - gripper changers can be used to make a robot multifunctional
  5. - multiple EOAT heads allow one robot to perform many different tasks without an EOAT change.
  6. - *** Don't try to mimic human behavior.
  7. - design for quick removal or interchange of tooling by requiring a small number of tools (wrenches, screwdrivers, etc).
  8. - provide dowels, slots, and other features to lead to fast alignment when changing grippers.
  9. - use the same fasteners when possible.
  10. - eliminate sharp corners/edges to reduce wear on hoses, wires, etc.
  11. - allow enough slack and flexibility in cables for full range of motion.
  12. - use lightweight materials, and drill out frames when possible.
  13. - use hard coatings, or hardened inserts to protect soft gripper materials.
  14. - examine alternatives when designing EOAT.
  15. - the EOAT should be recognized as a potential bottleneck, and given extra design effort.
  16. - use shear pins, and other devices to protect the more expensive components.
  17. - consider dirt, and use sealed bearings where possible.
  18. - move as much weight away from the tip of the gripper towards the robot.