IEEE Robotics & Automation Magazine - September 2013 - 68

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Figure 7. Robot motion in chairlike test structure.

Manipulation Motions (Robot R2)
R2 was designed to traverse a structure more robustly than R1
while adding the ability to manipulate the lockable truss connections. The robot demonstrated disassembly of a vertical
square and disassembly and reassembly of a vertical and horizontal rod. These actions are shown in the demo video that
accompanies this article.
Basic Motions
The three basic motions tested were translational motion, disassembly motion, and assembly motion. There are slight differences in the translational motions performed by robots R1
and R2 because of the use of stronger servos and the presence
of sensors in robot R2.
1) Translational Motion: The robot starting position has both
robot halves connected to rods with the translational
mechanism engaged. The robot is attached below a horizontal rod. The robot could also be attached on top of the
horizontal rod as an alternative starting point. The robot
then performs the steps, as shown and described in Table 4.
The robot completes the motion with both translational
mechanisms engaged at the center of the rod. The same
steps would be performed, but in reverse order, to advance
to the other end of the rod. Additionally, the same motion
and steps could be performed on a vertical rod with the
robot moving either up or down.
If the motion before or after the translational motion is
a disassembly motion, the initial or final steps vary slightly.
In the event that a disassembly just occurred, only one
translational mechanism is engaged. If the robot moves to a
rod with the intention to remove it, the robot will not
engage the second translational mechanism but instead
will start with the sequence to disassemble the rod.
2) Disassembly Motion: The disassembly motion starts with
one-half of the robot connected to a horizontal rod via its
68

IEEE ROBOTICS & AUTOMATION MAGAZINE

september 2013

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Figure 8. Disassembly and assembly motions: (a) vertical truss
structure disassembly and (b) disassembly/assembly of vertical rod.

translational mechanism. The second half is at the rod to
be disconnected. The robot then performs the steps as
shown and described in Table 4.
When the rotational mechanism is engaged, feedback
from the servos is used to gauge torque and rotation
amount applied by the cam actuator. These readings are
interpreted by the program to ensure proper rotational
engagement has occurred. The robot will automatically
realign, and re-engage itself until it has determined that the
attachment will likely result in a successful disassembly.
3) Assembly Motion: For the assembly motion, the robot
starts with one translational mechanism on one rod
and the opposite rotational mechanism holding the rod
to be connected to the node. The hinge is at an angle of
90°. The robot then performs the steps as shown and
described in Table 4.
4) Disassembly of a Horizontal Rod, 90° Rotation, and
Assembly at a Different Point of the Connector: This test
was done to verify that a rod can be disconnected at one
side of a connector and reconnected after a 90° rotation.
This test was performed only once as a demonstration

Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - September 2013