IEEE Robotics & Automation Magazine - December 2017 - 73

Swing

Hip Angle (rad)

0

Stance

0

-0.5

-0.5

-1

-1
-1.5

-1.5
0

0.2

0.4
0.6
Gait (%)

0.8

1

0

0.2

0.4
0.6
Gait (%)

(a)

Ankle Angle (rad)

Knee Angle (rad)

Swing
1.5

1.5

1

1

0.5

0.5
0.2

0.4
0.6
Gait (%)

0.8

1

0

0.2

0.4
0.6
Gait (%)
(d)

Swing

Stance
0.4

0

0

-0.4

-0.4
0.2

0

(c)

0.4

0

0.4
0.6
Gait (%)

0.8

1

0.8

1

Stance
2

0

1

(b)

2

0

0.8

0.8

1

0

0.2

0.4
0.6
Gait (%)

(e)

(f)
Desired

Estimated

Figure 9. The joint angles when ascending stairs with powered ankles; the shaded gray region represents the double-support state:
hip angle during (a) swing and (b) stance; knee angle during (c) swing and (d) stance; and ankle angle during (e) swing and
(f) stance.

same reasons offered regarding a passive joint. Having tested
with Mina v1 and X1, our pilot felt that Mina v2 was the most
comfortable exoskeleton he had tried to date, and he found
that the inclusion of the toe-off motion assisted greatly in
walking. Additionally, he reported that the toe-off motion
allowed him to shift more of his weight into the exoskeleton,
away from his crutches.
Our pilot took his first step in Mina v2 on 8 August 2016,
leaving approximately eight weeks of training time for the
competition. Because much of this time was spent tuning,
we believe that a new user could be able to competently
walk in Mina v2 after only a few days. This is, however, largely a function of the user's timidity, or lack thereof, with our
pilot being notably willing to try and fail throughout the
training process. We also believe that the inclusion of the
powered ankle greatly increased both the pilot's mobility and
speed of training, as it decreased his reliance on the crutches
and functioned to propel him forward when walking. When
coupled with the right attitude, this made for an expedient
training process.

Conclusions
This work presents Team IHMC's entry in the Powered
Exoskeleton competition at the 2016 Cybathlon, a competition designed to push the development of new exoskeleton technologies for paraplegics. Mina v2 is a new
exoskeleton developed by IHMC that includes powered
ankle plantar flexion, a feature not present in most other
orthotic exoskeletons. We utilize a custom ball-screw-
driven actuator with a modular design on all six joints,
allowing easier repair and maintenance. Our distributed
control architecture allows high-level trajectories to be
generated using an embedded computer in the backpack.
Our novel joint kinematic trajectory design centers on the
inclusion of a powered toe-off motion. When combined
with our unique parameterized swing-leg trajectory, the
pilot is able to utilize a powered toe-off motion to help
push off the ground and so improve performance. This
was used throughout all of the tasks in the competition to
start or continue walking, as well as to help power the pilot
up the ramp and stairs.
DECEMBER 2017

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IEEE ROBOTICS & AUTOMATION MAGAZINE

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73
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