Definition
Today faster and cheaper computer
processors make robots smarter and less expensive. Researchers are working to
make robots move and ‘think’ more efficiently. Although most robots in use
today are designed for specific tasks, the goal is to make universal which can
to do anything a human can do.
DEFINITION OF A ROBOT
DEFINITION OF A ROBOT
The definition of an industrial
robot given by the Robotics Industries Association (R.I.A.) is, ‘A
reprogrammable, multifunctional manipulator designed to move material parts,
tools, or specialized devices through variable programmed motions for the
performance of a variety of tasks’. ISO defines Robot as: ‘Robot is an
automatically controlled, reprogrammable, multi-purpose machine with several
reprogram able axes which is either fixed in place or mobile for use in
industrial automation application’.
END EFFECTORS
End effector is a device or tool
that’s connected to the end of a robot arm. The end effector is a part of robot
arm that is designed to inter act with the environment. The exact nature of
this device depends on the application of the robot. The structure of an end
effector and the nature of the programming and hardware that drives it depend
on the task the robot will be performing. Robotic end effectors are a device
that attaches to the robot arm and enables the general purpose robot to perform
a specific task. End-effectors function as robotic hands. These tools are
typically connected to robot flanges, such as wrists, to perform applications.
End effectors are also known as:
• Robotic accessories
• Robotic peripherals
• Robotic tools
• End of arm tooling (EOAT)
• Robotic accessories
• Robotic peripherals
• Robotic tools
• End of arm tooling (EOAT)
GRIPPERS
Gripper design considerations are
crucial in producing a functional and cost effective product for rehabilitation
applications. This gripper is designed to be mounted to any robotic arm, and in
particular, wheelchair mounted robotic arms that are used to enhance the
manipulation capabilities of individuals with disabilities that are using power
wheelchairs. Most grippers of similar objectives use two fingers for grasping,
but the dexterity of these fingers limit the use of the gripper. This project
attempts to provide a new design with enough dexterity to widen the range of
grasping tasks that are used in the Activities of Daily Living (ADL) in an
effort to improve performance and usability.
This work focuses on people who have
limited or no upper extremity mobility due to spinal cord injury or
dysfunction, or genetic predispositions. Robotic aides used in these
applications vary from advanced limb orthosis to robotic arms. Persons that can
benefit from these devices are those with severe physical disabilities, which
limit their ability to grasp and manipulate objects. These devices increase
self-sufficiency, and reduce dependence on caregivers.
The main objective of this work is to design and fabricate a
gripper that is capable of grasping various door handles and knobs, cylindrical
and spherical objects, tapered and conical objects, rectangular and odd-shaped
objects, sheets of paper, light switches and buttons, and other larger objects
up to four inches in width that are commonly used for activities of daily
living. As a criterion, the gripping force objective was set to roughly ten
pounds of force. The gripper was to be mounted on the end of a robotic arm
which was connected to a wheelchair. This factor limited the gripper’s
size and weight, so design ideas were kept simple but effective. 3-D models of
the considered designs were created using Pro/E and then later printed out to
scale using a Rapid Prototype printer for design adjustments before building
the actual gripper.
Background
There are many universal gripper
designs available in the market today with pneumatic, hydraulic or electric
actuation. The most important design consideration of grippers that are used
for ADLs is the safety of the operator. Kolluru et al discussed the design of a
reconfigurable gripper that consists of four fingers in a cross-bar
configuration as shown in figure 2.1. A suction based gripper unit was mounted
on each one of the fingers to handle limp material without causing any
distortion or deformation.
The reconfigurable gripper prototype
Figure 2.2 shows another design of a
reconfigurable gripper that was conducted by Yeung et al utilizing a wrench
system and multi-finger configuration to handle parts of different geometry
with different grasping points. This design was developed for robotic arms that
are used for assembly of automotive body parts.
A 6-DoF reconfigurable gripper
Specific considerations were taken
in the attempt to optimize the functionality of the gripper. It was decided
early on that the gripper would utilize parallel motion generated from a dual
four bar mechanism attached to each side of the two fingers creating 8 links
between the gripper surfaces and the driving mechanism itself. As a start, the
gripper’s fingers (paddles) were first put into consideration. Through the
required tasks expected out of the overall device the gripper’s surfaces were
designed to be varied for the adequate handling and use of household objects
mentioned. For those items, the profile was decided initially to be angled. The
angled surface was designed to constrain and secure handled objects, and the middle
opening was meant to secure spherical objects. When opening a spring-loaded
door, the two teeth at the tip of the paddles can secure the handle during the
robot motion, and make the grasping force independent of the closing force of
the gripper
Conclusions:
This work presented the design and
fabrication of a new custom designed gripper to help people with disabilities
perform activities of daily living. The intended work environment of this
gripper is to work with the newly developed Wheelchair-Mounted Robotic Arm
(WMRA) attached to a power wheelchair. Several design considerations were
studied to ensure a proper design is selected for the intended use of the
gripper. The paddles were designed with several contact surfaces with the
handled objects to handlelarge objects, spherical objects, cylindrical or
tapered objects, and delicate or small objects. The driving mechanism was
designed to be efficient and independent of the arm attached to it for
modularity and ease of use. Force propagation was conducted, and part selection
was done based on the analysis. The control system was chosen to be compatible
with the control of the WMRA system. Several tests were done on a prototype
prior to the production of the final gripper to adjust the design, and these tests
were conducted again with the actual gripper mounted on the WMRA system to
ensure its functionality as designed.
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