IEEE Robotics & Automation Magazine - December 2017 - 94

Wrist Interface
F
Electronic
Board

E
Actuation Lever
C
D

C
B

Motor

A

(a)

(b)

(c) Action: Push

(d) Action: Release

Push

(e) Action: Pull

Release
Switch
Mode

Voluntary Closing

Voluntary Closing

Pull

Pull
Hand
Closed

Hand
Open

Hand
Closed

Hand
Open

Release

Release

Release
Actions: Push, Release, and Pull

Switch
Mode

Push

(f)

Figure 5. (a) A computer-aided design model of the SHPH. (b) An exploded view of the
input lever; the input mechanism consists of A, the support part connected with D, the
lever using C, two bearings. B allows switching between different configurations, and
E is the cover of the whole system that is mounted to F, a rotary encoder. (c)-(e) The
input lever configuration in three different control situations: (c) pushing the lever to
switch modes (from VO to VC and vice versa), (d) releasing the lever to enter rest mode,
and (e) pulling the lever to activate the hand. (f) The logic of the input control algorithm
behind the mechatronic system.

94

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IEEE ROBOTICS & AUTOMATION MAGAZINE

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DECEMBER 2017

is covered by part E, on which a rotary
encoder F is mounted. The lever has a
small groove to house the end of the
Bowden cable of the shoulder harness.
Shoulder movement pulls the lever
down and activates the hand [see Figure 5(e)]. The lever returns to the rest
position thanks to an elastic band connected to the upper part of the mechanism. This system allows for the
translation of the Bowden cable movement into a motor command with a
considerable effort reduction compared to commercial BP devices (see
Table 3). An upgrade to this system,
implemented following the Cybathlon,
was the introduction of a switch B
between two different modalities with
a working principle similar to the
one presented in [23]. It is possible to switch between a voluntary
opening (VO) and a voluntary closing (VC) mode by pushing the lever.
The logic schema behind the switching
mode is depicted in Figure 5(f). It is
possible to manage the force (acting on
the lever spring) and shoulder movement (acting on the encoder range)
that are needed to activate the system.
These features can reduce shoulder
pain for the user but also allow the system to adapt to different users' needs.
Setting the force or the movement
needed for the activation allows the
system to provide some kind of exteroceptive and proprioceptive feedback to
the user, in a way similar to that of
conventional BP systems but decoupled from the grasp and functional
needs of the mechanical device (see
the "System Performance" section).
System Performance
Table 3 highlights some features of the
SHPH in comparison to two commercial BPPs [Ottobock (Austin, Texas)
Hook and Hosmer Soft VO hand]. As
shown, the SHPH needs a significantly
lower level of force for the activation
than the other two solutions. Empirical data show that the level of force
required to obtain a minimum opening is ten times less than the Ottobock Hook and 16 times less than the
Hosmer hand. Such reduction
becomes higher (14 times and 21 times,
Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - December 2017
