|
|
|
|
|
����������� At
the initial meeting in October 2000, representatives from both |
|
����������� The
2000-2001 design needed to be cheaper and lighter than that of Chris Fearon
and the 1999-2000 team.� Other
improvements that were to be implemented were to increase the lift capacity
of the arm and to have a fully functional control system.� By the end of the meeting, the 2000-2001
team members from both universities decided on the following parameters for
the new robotic manipulator: |
|
�
6
Degrees of freedom |
|
�
Maximum
weight of entire assembly less than 30 lbs. |
|
�
Fully-functional
control system with working user interface |
|
�
A
maximum linkage movement speed of 0.5 m/s |
|
�
Lift
a 1.5 kg (~3.3 lb.) mass |
|
�
Maximum
cost of $4000 including the controls |
|
|
|
����������� Due to the physical layout of the wheelchair, many
constraints had to be placed on the design to ensure that no clearance or
interaction problems would occur.� The
first constraint placed on the design was that no part of the assembly could
extend more than 6 inches beyond the furthest edge of the wheelchair (see
Figure 3.1).� This constraint was
placed to make sure that with the arm mounted on the wheelchair, the
wheelchair would still be able to fit through a standard doorway without too
much difficulty. �Another constraint
was that in the home position (see Figure 3.2), the arm was not taller than
and does not interfere with the armrest of the wheelchair or with the rear
tire.� The placement of the robotic arm
was also limited by a cross member of the frame of the wheelchair.� This cross member had to be taken into
consideration when selecting the placement and mounting widths of the
mounting brackets.� The final
constraint of the design was that no part of the assembly would interfere
with the swivel and rotation of the front tire.� This constrained the mounting height of the
arm and extension of any parts below the base of the arm. |
|
|
|
����������� Figures
3.1-3.4 show some different orientations of the completed 2000-2001 robotic
arm. |
|
|
|
|
|
����������� Early
in the project, it was realized that describing the different motions, parts,
and joints of the arm was difficult.�
Therefore, members of both teams decided to create a standard
terminology in order to make communication easier and less confusing.� The basis of the terminology was the human
arm.� The main parts of the arm were
chosen as the base, lower arm, forearm, and the gripper (see Figure
3.5).� The joints were defined as they
would be on the human arm, shoulder, elbow, and wrist.� The shoulder is the joint between the base
and the lower arm. The elbow is the joint between the lower arm and forearm.
Finally, the wrist is between the forearm and the gripper.� Since these three joints account for 5 of
the 6 degrees of freedom, the motion of each of the joints were added to the
terminology.� The shoulder joint was
broken into the shoulder twist and the shoulder bend motions (see Figure
3.6).� The shoulder twist is the motion
of the arm rotating around a vertical axis as viewed from the side of the
chair.� The shoulder bend is therefore
the motion of the lower arm rotating around a horizontal axis.� Since the elbow only has one degree of
freedom, its motion was simply defined as the elbow bend. (See Figure 3.7) �The wrist, like the shoulder, has two
degrees of freedom. (See Figure 3.8)�
The wrist bend motion refers to the rotation of the gripper around an
axis that is located at the end of the forearm and runs along the width of
the forearm tube.� The wrist twist
motion is the rotation of the gripper about an axis that runs along the
length of the forearm.� The sixth
degree of freedom is the clamping action of the gripper and is referred to as
the gripping motion. |
|
|
|
|
|
|
|
3.5 PERFORMANCE HIGHLIGHTS |
|
����������� The
final design of the 2000-2001 robotic arm has the following performance and
functional characteristics: |
|
o
Freedom
of Motion |
|
o
Shoulder
twist = 3600 |
|
o
Shoulder
bend = 2100 max. |
|
o
Elbow
bend = 2550 |
|
o
Wrist
twist = 3600 |
|
o
Wrist
bend = 1400 |
|
o
Length |
|
o
Shoulder
to Elbow = 15.5 in. |
|
o
Elbow
to Wrist = 14.56 in. |
|
o
Wrist
to Finger Tips (open) = 11.05 in. |
|
o
Full
Extension = 41.11 in. |
|
o
Width |
|
o
Extension
beyond the wheelchair width = 3.25 in. |
|
o
Wheelchair
width with the arm = 27.75 in. |
|
o
Vertical
Reach |
|
o
Above
the ground = 61.50 in. max. |
|
o
Below
the ground (plane wheelchair is sitting on) = 10.25 in. max. |
|
o
Horizontal
Reach |
|
o
Extension
from front wheel of the wheelchair = 38.11 |
|
o
Extension
from side of the wheelchair frame = 45.11 |
|
o
Total
Weight |
|
o
22
lbs. |
|
o
Lift
Capacity |
|
o
3+
lbs. |
|
The above values are actual values measured
from the final arm once it was completely assembled and mounted on the
wheelchair.� The design criteria, as
mentioned before, were not only met, but also exceeded in some areas.� |