What is a
gripper? Why use one?
A gripper
is a device that enables the holding of an object to be manipulated. The easier
way to describe a gripper is to think of the human hand. Just like a hand, a
gripper enables holding, tightening, handling and releasing of an object. A
gripper is just one component of an automated system. A gripper can be attached
to a robot or it can be part of a fixed automation system. Many styles and sizes
of grippers exist so that the correct model can be selected for the application.
What is the basic
operating principal of a gripper?
Compressed
air is supplied to the cylinder of the gripper body forcing the piston up and
down, which through a mechanical linkage, forces the gripper jaws open and
closed. There are three primary motions of the gripper jaws: parallel, angular
and toggle. These operating principals refer to the motion of the gripper jaws
in relation to the gripper body.
Parallel Gripper: The gripper jaws move in a parallel motion in relation to the gripper body. Used in a majority of applications, parallel grippers are typically more accurate than other style grippers.
Angular Gripper: The gripper jaws are opened and closed around a central pivot point, moving in a sweeping or arcing motion. Angular grippers are often used when limited space is available or when the jaws need to move up and out of the way.
Toggle Gripper: The pivot point jaw movement acts as an over-center toggle lock, providing a high grip force to weight ratio. This mechanism will remain locked even if air pressure is lost.
Differences
Between a 2-Jaw and 3-Jaw Gripper
2-Jaw
Gripper: The most popular style of gripper, all 2-jaw grippers (angular,
parallel and toggle) provide two mounting locations for the fingers that come in
contact with the part to be grasped. The jaws move in a synchronous motion
opening and closing toward the central axis of the gripper body.
3-jaw Gripper: A more specialized style of gripper, all 3-jaw grippers (parallel and toggle) provide 3 mounting locations for the fingers that come in contact with the part to be grasped. The jaws move in a synchronous motion opening and closing toward the central axis of the gripper body. 3-jaws provide more contact with the part to be grasped and more accurate centering than 2-jaw models.
Internal vs.
External Gripping
Grippers
are used in two different holding options: external and internal. The option
used is determined by the geometry of the part to be grasped, the process to be
performed, orientation of the parts to be grasped and the physical space
available. External: External gripping is the most common way to hold parts. The
closing force of the gripper is used to hold the part. Internal: Internal
gripping is used when the part geometry will allow and when the process to be
performed need access to the outside surface of the part grasped. The opening
force of the gripper is used to hold the part.
Tooling/Finger
Design Considerations
Custom
gripper tooling/fingers are needed for each application. Fingers are used to
actually make contact with the part to be grasped. Careful consideration when
designing these fingers can greatly reduced the size and grip force of the
gripper needed for the application. The encompassing or retention finger shape
is preferred because it increases stability and also reduces the necessary grip
force. However, the additional jaw travel required to encompass or retain the
part must be taken into consideration.
Rotary Actuators
What is a rotary
actuator? What does it do? The rotary actuator is a device used to alternate the
rotated position of an object. Just like the human wrist the actuator enables
the rotation of an object, except that rotary actuators are available in a wide
variety of models with different sizes, torques and rotation angles. The energy
for the rotation is delivered by pneumatic pressure. The rotary actuator
converts the air pressure from a linear motion to a rotating motion. What is the
basic operating principal of a rotary actuator? The rotary actuator converts the
air pressure from a linear motion to a rotating motion. This is done by a rack
and pinion. Air pressure is supplied pushing the piston in a linear motion,
attached to the piston is a straight set of gear teeth called a "rack." The rack
is pushed in a linear motion as the piston moves. The gear teeth of the rack are
meshed with the circular gear teeth of a "pinion" forcing the pinion to rotate.
The pinion can be rotated back into the original position by supplying air
pressure to the opposite side of the air cylinder pushing the rack back in the
other direction. The pinion is connected to a shaft that protrudes from the body
of the rotary actuator. This shaft can be connected to various tools or
grippers.
Authored by Applied Robotics.
For more information contact:
Applied Robotics, Inc.
648 Saratoga Road
Glenville, NY 12302
518-384-1000
Fax: 518-384-1200