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11.1 END OF ARM TOOLING (EOAT)
•The best known universal gripper - the human hand
•Useful classifications are,
-Grippers
-multiple/single
-internal/external
-Tools
-compliant
-contact
-non-contact
•End of arm tooling is typically purchased separately, or custom built.
11.1.1 EOAT Design
• Typical factors to be considered are,
Workpiece to be handled part dimensions mass
preand postprocessing geometry geometrical tolerances
potential for part damage Actuators
mechanical vacuum magnet etc.
Power source of EOAT electrical pneumatic hydraulic mechanical
Range of gripping force object mass
friction or nested grip
coefficient of friction between gripper and part maximum accelerations during motion
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Positioning
gripper length
robot accuracy and repeatability part tolerances
Maintenance
number of cycles required
use of separate wear components design for maintainability
Environment temperature humidity
dirt, corrosives, etc. Temperature protection
heat shields longer fingers
separate cooling system heat resistant materials
Materials
strong, rigid, durable fatigue strength
cost and ease of fabrication coefficient of friction suitable for environment
Other points
interchangeable fingers design standards
use of mounting plate on robot
gripper flexible enough to accommodate product design change
•The typical design criteria are,
-low weight to allow larger payload, increase accelerations, decrease cycle time
-minimum dimensions set by size of workpiece, and work area clearances
-widest range of parts accommodated using inserts, and adjustable motions
-rigidity to maintain robot accuracy and reduce vibrations
-maximum force applied for safety, and to prevent damage to the work
-power source should be readily available from the robot, or nearby
-maintenance should be easy and fast
-safety dictates that the work shouldn’t drop when the power fails
•Other advanced design points,
-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.
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robot arm |
Part |
|
|
|
Gripper |
Better - less chance of slippage |
- holding pressures/forces/etc are hard to control, try to hold parts with features or shapes
robot arm |
Part |
Gripper |
part will be more stable, and well located |
-compliance can help guide work into out-of-alignment conditions.
-sensors in the EOAT can check for parts not in the gripper, etc.
-the gripper should tolerate variance in work position with part alignment features
-gripper changers can be used to make a robot multifunctional
-multiple EOAT heads allow one robot to perform many different tasks without an EOAT change.
-*** Don’t try to mimic human behavior.
-design for quick removal or interchange of tooling by requiring a small number of tools (wrenches, screwdrivers, etc).
-provide dowels, slots, and other features to lead to fast alignment when changing grippers.
-use the same fasteners when possible.
-eliminate sharp corners/edges to reduce wear on hoses, wires, etc.
-allow enough slack and flexibility in cables for full range of motion.
-use lightweight materials, and drill out frames when possible.
-use hard coatings, or hardened inserts to protect soft gripper materials.
-examine alternatives when designing EOAT.