IEEE Robotics & Automation Magazine - September 2016 - 39

Actuators made with polymermolded units were also tested. For
actuators made with five polymermolded independent bending units,
the force was almost 49 mN at from 5
to 15 kPa of air pressure. This is
because the units were connected
with soft and flexible bistable junction
connectors. However, actuators made
with five polymer-molded cooperating bending units exerted a maximum of 418.6 mN force at 7 kPa of air
pressure. This difference occurred
because cooperating bending units
have greater structural constraints
than independent bending units. In
the future, we will optimize the design
of the polymer-molded bistable connectors, which we hope will improve
the force characteristics of units assembled with bistable connectors.

10 mm
(a)

(b)

(c)

(d)

10 mm
(e)
Bending Unit
for Crawling

(f)

(g)

Bending Unit
for Steering

Reliability and Fatigue
Characteristics of Units
The reliability and fatigue of bending
and translating actuators assembled
with different kind of units were tested.
100 mm
The experimental setup was prepared
Soft,
3-D-Printed Unidirectional
Bistable Junction
Parts
with a feedback control system [FigWheel
ure  10(b)]. During the fatigue tests,
(h)
(i)
pressure was applied up to a target
value for one cycle, held for about 1 s,
then ventilated [Figure 10(b)].
Reliability testing was performed
first. The highest applied pressure,
which was used in displacement performance tests, was set as the target
pressure for each type of bending and
translating actuator. Bending actuators and translating actuators made
(j)
with five 3-D-printed units were
fatigue tested with this target pressure
for 500 cycles, and they failed at Figure 11. Rapidly prototyped structures and applications using various shapes of units.
(a )-(d) A gripper built with 3-D-printed cooperating bending units and rigid connectors.
around 350-500 cycles. However, (b) and (d) This gripper could grasp a 33.2-g square box and a 3.7-g paper cup at 20 kPa
thanks to our modularized design of air pressure. (e) Four-unit and, (e) and (f), eight-unit grippers built with independent
concept, the failed actuators could be bending units with bistable connectors for grasping different sizes of objects. (h) A
crawler prototyped with soft modules. (i) The crawler turns by inflating the module in the
quickly repaired by changing only center of the robot. (j) The robot crawls forward by simply inflating its legs (the crawler's
speed was 603 mm/min, or 2.3 body lengths/min).
their failed units.
To avoid the failure of units during fatigue-test cycles, fatigue tests
were performed with target pressures at around half of the with five polymer-molded independent bending units,
highest pressures. Figure 10(d)-(h) shows the results of respectively. As the graphs show, the deformation characfatigue tests for actuators made with five 3-D-printed teristics of 3-D-printed actuators and polymer-molded
cooperating bending units, with five 3-D-printed indepen- independent bending units were almost the same at the
dent bending units, with five 3-D-printed translating units, first cycle and after 300 and 600 cycles of pressurizing and
with five polymer-molded cooperating bending units, and ventilations, respectively.
September 2016

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Ieee rObOtICS & AUtOmAtION mAGAZINe

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Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - September 2016
