Instrumentation & Measurement Magazine 25-9 - 37
Fig. 1. Setup used for the study of the kinematics of ant locomotion.
C=camera; W=walkway; IR=infrared strobe.
locomotion in a 20x20x250 mm volume with a 0.0096 mm/
pixel resolution, with on average, 3% (i.e., 0.03 mm error on a
1mm measure) resolution in each dimension of the volume (including
tracking and pattern recognition errors). The locations
of 47 anatomical marks for body extremities and articulations
between the different body segments (Fig. 2d) were then determined
in an external 3D coordinate system using the software
Vicon Peak Motus 10.0 (http://www.motus10.com/). Since
the number of points we tracked on the ants was significant,
and the videos were captured at a high frame rate, this tracking
process can be extremely time-consuming. The recently developed
deep-learning based approach to automatically track
points looks very promising for reducing the time dedicated to
the tracking of insects' anatomical marks [2].
Unfortunately, at the end of the experiment, it was necessary
to humanely kill the ants so that the mass of their three
main body segments (head, thorax, and gaster) could be
measured. With this information and the positions of the extremities
of those segments, the position of the center of mass
(CoM) for each ant could be approximated. This allowed us to
study the dynamics of the overall CoM of the ants in different
conditions, e.g., when an ant is walking unladen or bearing a
load in its mandibles [5]. Based on high-resolution images of
the ant exoskeleton acquired through X-ray microtomography,
we were then able, by using the free open source software
Opensim (https://opensim.stanford.edu/), to characterize
the different types of articulation between body segments and
between the parts of the legs, and to integrate this information
into a 3D ant kinematic model. Using an inverse kinematic
optimization process, this 3D model subsequently allowed
us to reduce the errors due to tracking and pattern matching
recognition [6]. By considering an ant as a polyarticulated system
composed of 40 articulated solid segments, one can then
calculate several kinematic parameters such as the segment
Fig. 2. (a) Vertical position of the joints in the 3D ant kinematics of the middle leg over time; (b) Vertical velocity of the joints; (c) Accelerations of the joints; (d)
Segments and joints are computed in the external frame using a kinogram. Cox-Tro= coxa to trochanter joint; Tro-Fe= trochanter to femur joint; Fe-Ti= femur to tibia
joint.
December 2022
IEEE Instrumentation & Measurement Magazine
37
https://opensim.stanford.edu/
http://www.motus10.com/
Instrumentation & Measurement Magazine 25-9
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