IEEE Robotics & Automation Magazine - December 2014 - 39

displacement) in a bidirectional mode over a wide range of
motion of the output link. This configuration makes it possible to achieve a constant speed reduction ratio of 1:101 with
an average mechanical efficiency of 86% (more details, including dynamic characterization of this actuation configuration, are reported in [19]).
Configuration A is implemented in two different sizes:
1) a high torque version in which the components are dimensioned for a target output nominal torque of 500 Nm, employed for the actuation of joints J l3, J l4, J l5, J a1, and J a2
2) a low-torque version in which components are dimensioned for a target output nominal torque of 290 Nm, employed for the actuation of joint J a3 .
Configuration B
In Configuration B, the rotational motion of the motor is first
converted into a linear motion through a ball-screw drive and
then reverted back to rotational by an inverted slider crank
mechanism [Figure 4(b)]. This configuration features a nonconstant speed-reduction ratio and a limited range of motion
of the output. Diverse implementations, which differ in the dimensions of crank and connecting rod, have been conceived
to match the various joint requirements in terms of torque, velocity, and range of motion. Configuration B is employed for
the actuation of joints J l1, J l2, J l6, and J a5 .
Configuration C
In Configuration C, the motor is coupled with the output
axis through a gear train reducer implementing a speed reduction ratio of 1:160 [Figure 4(c)]. This is obtained through
a double stage reduction with the idler gear coupled to a
large-diameter hollow driven gear that surrounds the forearm of the user. The Configuration C is employed only for
the actuation of joint J a4 .

Idler Gear

Ball-Screw
l-Screw

Actua
Actuator

tuator
Actuator
Jl66

Pantograph
aph
Mechanism
sm
m

Jl5

Pini
Pinion

Ja44
Ball-Screw

Cables
Jl3

Driven Gear

Foot

(a)

(b)

(c)

Figure 4. The CAD representation of the actuation configurations:
(a) configuration A, (b) configuration B, and (c) configuration C
(photo courtesy of the PERCRO Laboratory, TeCIP Institute,
Scuola Superiore Sant'Anna).

The Gripper
The end-effector of the
BE is equipped with a
The BE employs five force
dual parallel jaw gripper.
One of the jaws (Figures
sensors, one for each
1, 5, and 6) is fixed with
respect to link 4 of the
contact point with the
arm. Jaw movement is implemented through a paruser's body.
allelogram mechanism
that is activated by an actuator mounted according to Configuration B. The closing
command is provided by a sensorized trigger lever that is controlled by the closing movement of the user's hand.
Remote Center of Rotation
Joint J l2 passes through the center of the user's hip and is implemented through the remote-center-of-rotation mechanism as shown in Figure 4. This allows the leg of the BE to
keep adherence to that of the user, particularly during operations that require the system to turn in place. This feature
is especially desired when operations are conducted in narrow spaces.

Mechanical Design Details
The detailed design of the mechanical components of the BE
has been conducted with the
aim of minimizing the overall system mass through strucBackpack
Snowboard
Force Sensor
Frame
tural optimization. A further
Force Sensor
Shoulder
Bindings
(Type 2)
important issue that has been
(Type 1)
Straps
considered is the mass distribution, which has been placed
so as to guarantee stability during static walking, as demonWaist
strated in the simulation [20].
Belt
In this section, some of the
relevant mechanical details of
1-DoF Trigger
Common
Force Sensor
the BE are highlighted, inwith Gripping
Footwear
(Type 1)
Force Sensor
cluding 1) the gripper, 2) the
remote center of rotation em(a)
(b)
(c)
ployed for the implementation of the leg joints J l2, and Figure 5. Solutions for connecting to the human limbs and back: (a) a snowboard binding for the
foot; (b) a plastic backpack frame with shoulder straps, a lower back pad, and a waist belt for the
3) the attachments to the torso; and (c) the custom-made gripping handle equipped with a trigger for the hand (photos
wearer's body.
courtesy of the PERCRO Laboratory, TeCIP Institute, Scuola Superiore Sant'Anna).
December 2014

IEEE ROBOTICS & AUTOMATION MAGAZINE

Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - December 2014