情報処理学会 インタラクション 2023
IPSJ Interaction 2023

3B-46
2023/3/1

Variable Stiﬀness Shape-changing Interface using
Artiﬁcial Muscle
Jefferson Pardomuan1,2

Shio Miyafuji1

Hideki Koike1

Abstract: In this paper, we explore the implementation of variable stiﬀness for shape-changing interface
applications. We proposed a stiﬀness control mechanism using a combination of Pneumatic Artiﬁcial Muscle(PAMs) and 3D-printed reinforcement. The three reinforcements include a locking module, a plastic
deformation module, and a rotational brake module. We demonstrate the feasibility of this mechanismthrough ﬁve application examples and conclude with a discussion.

Related Work

The common technique of variable stiﬀness is the vacuum
jamming technique which includes granular, layer, and ﬁber
jamming [2], [3], [4]. These stiﬀness control techniques areable to exert a high degree of stiﬀness change. However, it
is not easy to combine the shape-changing actuation withthe jamming mechanism due to the complexity of multiple
actuator control [5]. In this paper, we proposed a convenient
control system, where both shape deformation and variable
stiﬀness actuation are combined in one mechanism.
Deployability is a useful feature for the shape-changing interface. Some advantages of the deployable interface are thestoring easiness, increased change in durability, and adaptability to various environments. Previous work has proposed
12

Tokyo Institute of Technology
jeﬀerson.pardomuan@gmail.com© 2023 Information Processing Society of Japan

3D DESIGN

Plastic Deformation

Rotational Brake

BUNACTUATED[0 kPa]Variable stiﬀness is a beneﬁcial feature for a computerinterface because it can exponentially increase the interaction and utilization possibility. In previous work on soft
robotic applications, a gripper that can grasp various objects by changing the gripper stiﬀness has been proposed [1].
It shows how the interface can adapt to both environment
and the target object eﬀectively, with little control and energy cost. Although previous works have proposed some applications of variable stiﬀness for computer interface[2], [3],the capabilities of both shape and stiﬀness change simultaneously have yet to be fully explored. In this paper, wedevelop a shape-changing interface with variable stiﬀnesscapabilities. We utilize Pneumatic Artiﬁcial Muscle(PAMs)
as actuators and 3D printed reinforcement to alter the actuation force into shape and stiﬀness change. Employing
these features, we introduce ﬁve shape-changing interfaces
application.

2.

Locking

Introduction

ACTUATED[400 kPa]

1.

Fig. 1

Variable stiﬀness behavior related with reinforcement
modulesa soft robot that can be deployed for rescue purposes[6].
NinjaTrack and PuPoP[7], [8] are user interfaces that canbe deployed by the user at will or through some interaction.
Poimo [9] is a mobility device that can be collapsed to be
stored easily.

3.

Design and Implementation

We design three types of reinforcement including locking,plastic deformation, and rotational brake. Variable stiﬀness
is achieved by altering both the contraction force and expansion force of the PAMS.
( 1 ) Locking module is based on the beaded jamming phenomenon. We use the contraction force of PAMs to tension an array of hollow modules, and interlock them toeach other.
( 2 ) Plastic deformation module has unique behavior
which allows the structure to retain its shape after being bent by an external force.
( 3 ) Rotational brake module is based on a hinge structure with PAMs as its shaft. When PAMs is unactuated,

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情報処理学会 インタラクション 2023
IPSJ Interaction 2023

3B-46
2023/3/1

Collapsed

Deployed(A)

Electropneumaticregulator

DAC

Air tank

Microcontroller

Air Compressor

PC

Fig. 2

Pneumatic control diagram

(B)

(C)

(D)

(E)

Fig. 4
Fig. 3(A) Crumbled device, (B) Incapacitate device, (C) Flaten
device, (D) Deformable device, (E) Fabric-like device

Air pressure and stiﬀness control relationshipthe hinge can rotate freely. However, when PAMs are
expanded inside the hinge, they will rub together andresist rotation.
3.1 Fabrication
Our proposed system only consists of 3 parts: pneumatic
artiﬁcial muscles(PAMs) as actuators, 3D printed structures
as reinforcement, and compressed-air controls. To fabricate
reinforcement structures, users can use both FDM and SLA
3D printers. The material used mostly rigid ﬁlaments suchas PLA and ABS, however for bending modules, we use ﬂexible ﬁlament TPU95. After 3D printing, the user assembles
the reinforcement similar to beads craftworks. Here manual
work of threading PAMs through holes in reinforcements isneeded.
3.2 Control
Both the deformation state and stiﬀness level is controlled
by air pressure. The air pressure controlled by the electropneumatic regulator ranged from 0 0.4 MPa. We conduct atechnical evaluation to investigate the relationship between
stiﬀness change and air pressure. Figure 3 shows the stiﬀness control range for each module.

© 2023 Information Processing Society of Japan

4.

Application

Here, we demonstrate the application of variable stiﬀnessfeatures on shape-changing interfaces.
4.1 Crumbled deviceFigure 4(A) shows glasses that can be softened into a totally ﬂexible state. In this state, the device can be crumbled
without breaking and easily stored inside a small pocket.
When actuated, it instantly returned to a normal glasses
shape.
4.2 Incapacitate device
Figure 4(B) shows a steering-wheel concept that can detect when a thief tries to steal the car. In that case, thedevice can incapacitate by collapsing the structure, making
the thief unable to control the wheel.
4.3 Flaten device
Figure 4(C) shows a vector equilibrium structure thatcan be ﬂattened when unactuated. In a ﬂattened state, it
can go through narrow space. When deployed, the structure
can carry a pratical load of up to 2kg.

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情報処理学会 インタラクション 2023
IPSJ Interaction 2023

4.4 Deformable device
Figure 4(D) shows a cube structure that consists of theplastic deformation module. When actuated, at ﬁrst it will
construct a cube structure. Additionally, the shape can be
deformed by the user freely due to the shape-retaining capabilities.

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2023/3/1

nology. ACM.

4.5 Fabric-like device
Figure 4(E) shows a fabric-like device that consists ofrotational brake modules in a grid structure. The device issoft and ﬂexible in the normal state, and malleable when
actuated. It can be utilized for wearable devices such as
medical casts where users can easily stiﬀen or soften it to beeasily removed.

5.

Discussion

In this paper, we did not implement sensors for interaction. However, the already installed air-pressure sensors andadditional sensors such as acoustic, optical, and contact sensors can be utilized. The sensor can be inserted into the 3D
printed substrate or embedded into the PAMs ﬁlament.
Currently, we only implement small-size devices with dimensions of up to 300 x 300 mm. In the future, room-size
structures with deployability functions can be implemented.
However, a computer simulation to calculate the optimized
truss frame, load endurance, and shape deformation will beneeded ﬁrst.
Although our system is not suitable for practical application due to the pneumatic device shortcoming, where it
needs a heavyweight compressor and power source. We believe that this technology problem will be resolved in thenear future. In this stage, our vision is to explore the new
possible application, as it will motivate progress in core technology such as materials, actuation, sensing, and energy.
References
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