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are rubber-lined, whereas the VEX
gripper has two concave curved
gripper fingers that are also rubber
lined. On first glance, with its two
parallel sides, this type of gripper
would seem to be ideal for grasping
flat objects or items with two flat and
parallel sides. Parallel jaw grippers do
have one disadvantage when trying to
grasp an object: The sides of the two
fingers/pincers of the gripper may not
exactly grab the sides of a square
object due to a slight difference in
‘parallelism.’ This will allow the object
to twist and swivel on the two points
of contact. Having a bit of ‘slop’ in
the construction of the two jaws and
the drive gears, or having compliant
rubber lining on the jaws will allow
full contact on both sides. The
Robotiq gripper shown in Figure 11
utilizes a unique finger configuration
to perform as a parallel jaw or V-jaw
gripper.
There are numerous styles,
quality, and prices of grippers that can
be found on major robotics
manufacturer’s sites and the overseas
Internet sites you can find when
Googling “robot grippers.” ServoCity
offers a line of four grippers shown in
Figures 12A to 12D priced from
$6.99 to $14.99. I would highly
recommend that any robot designer
peruse the pages of the
servocity.com site to look at the
many hundreds of photographs
showing mechanisms, structures,
bearings, and, of course, mountings
for all sorts of mechanisms including
these grippers.
Even if you don’t intend to
purchase any of their products, you
will most certainly see drawings and
photos that will make you say “why
didn’t I think of that?” I have collected
most of the photos into one file that I
refer to on many occasions when I am
trying to design something.
The V-Jaw Angle
Robot Gripper
One of the most common types
of gripper is the type that is formed
by two pincers opening and closing as
a “V” — like our fingers. The ServoCity
micro gripper utilizes a Hi Tec HS-
5055MG or similar sub-micro servo
and is a great gripper for small to tiny
robots. The ServoCity perpendicular
gripper is well suited for a mid-sized
robot, and the perpendicular oriented
servo mounting allows for a slender
arm structure.
The ServoCity horizontal gripper
utilizes the same V-gripper design as
the previous two with a horizontally
mounted servo, and they both can be
adapted to ‘standard’ Hi Tec or Futaba
servos.
All of these grippers are well
designed and built from stout 1/4”
ABS plastic. ServoCity also has a
mobile robot with an arm and gripper
that they call the Stacker (shown in
Figure 13) that I have yet to try out.
These grippers will always grasp
an object in two points, and the
object may swivel like the above
parallel jaws.
Again, the use of a rubber
compound on the faces of the two
fingers may stabilize the grasped
object. I used two soft rubber
replacement handle covers for needle-nose pliers on the jaws of the V-jawed
gripper on the robot in Figure 9.
The Parallel Jaw
Robot Gripper
The ServoCity parallel gripper
shown in Figure 12D has 2-1/2”
parallel jaws that spread to 2-3/4” and
only uses a standard Hi Tec servo. Just
Figure 13.
ServoCity
Stacker mobile
robot and arm.
Figure 14. The Tetrix
parallel jaw gripper.
Figure 12B.
ServoCity
perpendicular
gripper.
Figure 12C. ServoCity
horizontal gripper.
Figure 12A. ServoCity
micro gripper.
Figure 12D.
ServoCity parallel
gripper.