IEEE Robotics & Automation Magazine - December 2020 - 68

decrease in the bending force, which could be due to some
unintended motions often present in longer soft bending
actuators. Then, the actuator with two series of pouch motors
was compared to a variation of the base actuator [Figure 2(h)]. In this variation, the lateral constraint between two
serially connected pouch motor patterns was removed as well
as one of the pouch motors connected to it [Figure 2(i)]. The
goal of this variation was to maintain the bending force of the
actuator while significantly decreasing the bending angle created between successive patterns of pouch motors, as
it could be noticed that the bottom constraints remained
nearly flat.
Implementation as a Robotic Finger
One of the interesting aspects of the design is that the
dimensions of a single pattern of pouch motors will

determine the properties of this specific set of motors
without affecting the following one. Thus, it is possible to
change the deformed shape of the actuator by changing the
dimensions of the pouch motors and constraints throughout its length. Two actuators were built from a series of
four pouch patterns, where one had constant pattern
dimensions throughout and the other had varying ones
[Figure 3(a) and (b)]. The two central pouch motor patterns contained four pouch motors each, while the base
and tip patterns contained only three motors, to make it
easier to fix the finger, and did not affect the bending angle
or force in this implementation. The two actuators were
built such that the total length of the pouch motors and
constraints was equal between both. However, the dimensions of all elements in the second actuator were varied
throughout the length, while proportionally scaling all

Actuator
Fixation

0°

F/T
Sensor

90°

Angle
Guide

180°

Outer Layer
Pouch Motor
(l, D)

Lateral
Constraint (L1)

Slide

30
45
60
75
Bending Angle (°)
(d)
50 mm Width
One Pattern
50 mm Width
Two Patterns

60

kP
a
kP
a
40 k
Pa

50

30 kPa

20 kPa
10 kPa

0

30

60
90 120 150
Bending Angle (°)

Bending Force (N)

90

Bending Force (N)

Bending Force (N)
Bending Force (N)

15

180

(g)

40
35
30
25
20
15
10
5
0

40
35
30
25
20
15
10
5
0

a
kP a
kP
50

0

30 kPa
35 kPa
40 kPa
45 kPa
50 kPa
55 kPa
60 kPa

60

40
35
30
25
20
15
10
5
0

(b)
5 kPa
10 kPa
15 kPa
20 kPa
25 kPa

Bottom
Constraint (L2)

l : 50 mm, L1: 30 mm, L2: 30 mm

(a)
40
35
30
25
20
15
10
5
0

Inner Layer
Pouch Motor
(l, D)

40

30

kP

a

kP

(c)
Parallel Variation

50 mm Width
One Pattern
100 mm Width
One Pattern

D: 50 mm
One Pattern

a

20
10

D: 100 mm
One Pattern

kP

a

kP

a

0

15

30
45
60
75
Bending Angle (°)
(e)

90
(f)
Series Variation

60

kP
a
50
kP
a
40 k
Pa

50 mm Width
Two Patterns (Variation)
50 mm Width
Two Patterns

D: 50 mm
Two Patterns
D: 50 mm
Two Patterns
(Variation)

30 kPa

20 kPa
10 kPa

0

30

60
90 120 150
Bending Angle (°)
(h)

180
(i)

Figure 2. (a) The jig for testing the bending force. (b) The motion of the testing jig for different bending angles. (c) The dimensions.
(d) The actuation properties of the base actuator. (e) The actuation properties of the base actuator and an actuator with double the
width. (f) The top-view of the two actuators. (g) The actuation properties of the base actuator compared to an actuator with two units
in a series. (h) A comparison of the actuator with two units in a series to an actuator with a modified pattern. (i) The side-view of the
two actuators.

68

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IEEE ROBOTICS & AUTOMATION MAGAZINE

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DECEMBER 2020
IEEE Robotics & Automation Magazine - December 2020

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