Summary and critique of the article by Professor Wood and his
colleagues
Seitz, Benedikt F., et al, “Bio-inspired mechanisms for
inclined locomotion in a legged insect-scale robot.” Harvard Microrobotics
Laboratory. 14 December, 2014.
The
development of insect-scale robots has made a lot of progress in flat surface movements.
However, locomotion of the insect-scale robots on slanted surfaces has not been
as successful. This paper explores the use of different adhesion and alignment
mechanisms on the Harvard Ambulatory Microrobot (HAMR), the model insect-scale
robot for this experiment. The legs of the robot must exert enough peak and
normal forces on the surface to prevent slipping. Therefore, the different
adhesion methods must be tested for a degree of stability.
The
components to of the HAMR were carefully analyzed and tested to ensure the best
performance of the robot. The design of the actuator of the HAMR was selected
after testing different thicknesses of the various actuators. The 2-ply
actuator was determined to have the best mechanical advantage. Also the transmission
performance of the legs of the HAMR was tested. The locomotion of the legs was
then analyzed; it was found that the motion of the legs as they took steps was
not ideal for climbing inclined planes, as the robot rocked back and forth on
the legs that were in contact with the ground as the other legs were moving. In
order to compensate for this unwanted motion, a passive tail was added to the
HAMR so that its motion would be more stable.
There were
three types of adhesion methods that were tested: electroadhesion, micro-spine
adhesion, and gecko-like dry adhesion. The HAMR’s performance using these
adhesion methods was recorded.
In
testing the three methods, the HAMR was programmed to simulate walking on a
flat surface. The peak shear force (x-direction) and peak normal force
(z-direction) were recorded for each adhesion method. The directional gecko
adhesive resulted in the highest average shear force, while the
electro-adhesive material resulted in the highest average normal force.
Then,
the adhesion methods were tested in a climbing test. Each adhesive was tested
for the maximum incline and decline angle for which slipping would not occur.
The gecko dry adhesive, h = 100um, resulted in the greatest angle for incline
and decline – 22 and 45 degrees, respectively.
The
paper presents an exploration of ways to design locomotion on inclined planes
for insect-scale robots. By comparing the performances of the three adhesion
methods, the experiment clearly showed why one was more effective than the
other. The data and conclusions agree with each other – the gecko dry adhesive
had the largest maximum angle without slipping. The data and conclusions
address the limitations of certain aspects of the experiment, as well. The
micro-spine feet have a limited trajectory, and thus the trajectory must be
adjusted to create an adhesive force. This acknowledgement is thorough and
provides room for improvement in future experiments. Also, the analysis of the
original HAMR and corrections to its mechanics, such as adding the tail, was
very important to the overall experiment.
Possible
future experiments include using a combination of different adhesives to
achieve maximum attachment to inclined surfaces. I would also suggest that
future experiments include the same peak/normal force test and climbing test,
but with slightly different specifics – for example, alter the h value for the
gecko dry adhesive. I found it very interesting and helpful to see an example
of hybrid adhesion systems in nature – the Oecophylla
smaragdina ant’s foot. This shows that the idea of the insect-scale robot’s
hybrid adhesion systems is modeled after something found in the natural world.
