ABioinspiredStiﬀnessTunableSuckerforPassiveAdaptationandFirm Attachment to Angular Substrates Arman Goshtasbi

2025-04-30 0 0 4.02MB 14 页 10玖币

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A Bioinspired Stiﬀness Tunable Sucker for Passive Adaptation and Firm

Attachment to Angular Substrates

Arman Goshtasbi

Department of Biomechanical Engineering

University of Twente

Enschede, The Netherlands

a.goshtasbi@student.utwente.nl

Ali Sadeghi

Department of Biomechanical Engineering

University of Twente

Enschede, The Netherlands

a.sadeghi@utwente.nl

Abstract

The ability to adapt and conform to angular and uneven surfaces improves the suction cup’s

performance in grasping and manipulation. However, in most cases, the adaptation costs lack

of required stiﬀness for manipulation after surface attachment; thus, the ideal scenario is to have

compliance during adaptation and stiﬀness after attachment to the surface. Nevertheless, most

stiﬀness modulation techniques in suction cups require additional actuation. This article presents a

new stiﬀness tunable suction cup that adapts to steep angular surfaces. Using granular jamming as

a vacuum driven stiﬀness modulation provides a sensorless for activating the mechanism. Thus, the

design is composed of a conventional active suction pad connected to a granular stalk, emulating

a hinge behavior that is compliant during adaptation and has high stiﬀness after attachment is

ensured. During the experiment, the suction cup can adapt to angles up to 85◦with a force lower

than 0.5 N. We also investigated the eﬀect of granular stalk’s length on the adaptation and how this

design performs compared to passive adaptation without stiﬀness modulation.

1 Introduction

Adaptation plays a pivotal role in grasping, manipulating, and interacting with unknown environments. Due to

their low mechanical ﬂexibility, conventional robots require complex control and sensory and actuation systems

to achieve such adaptation [1]. In most cases, these robots lack adaptability and are only suitable for a single

task [2]. On the other hand, inspired by animals’ inherent ability to adapt to unknown surroundings, studies

suggest that soft grippers, thanks to their compliance, can exceed rigid robots’ limitations and perform more

adaptively in undeﬁned conditions [3].

Many animals utilize astrictive prehension, also known as adhesive grippers, to attach to surfaces or grab

objects. Diﬀerent techniques have been suggested to achieve adhesion inspired by such animals. For instance,

arXiv:2210.14818v1 [cs.RO] 26 Oct 2022

diﬀerent grippers have been developed using van der Waals force inspired by microﬁbers on gecko’s toes [4],

[5]. However, controlling the force in such grippers is diﬃcult [6]. Another technique, inspired by suction cups

in octopus tentacles [7], and suction disc on northern clingﬁsh ventral side [8] [9], is surface attachment using

negative ﬂuid pressure in a suction cup. Due to their fast, controllable, and eﬃcient way of attaching to surfaces

[10], vacuum suction grippers have shown great potential in various grasping applications, such as surface

grasping in wall-climbing robots [11], grasping in surgical application [12], and haptic exploration [13]. The

suction cups are either passive, in which the change in the shape provides negative pressure, or active, in which

an external vacuum pump generates the pressure. The active vacuum gripper produces more grasping force

and is easier to detach by connecting it to ambient pressure. At the same time, the latter provides a tetherless

solution and a more energy-eﬃcient solution for grasping [10].

Despite the numerous advantages of suction cups, conventional suction cups have some limitations in adaptation

to various environments. For instance, rough and porous surfaces prevent the vacuum suction cups from

providing negative pressure. Several studies have proposed designs to overcome these shortcomings by looking

at how animals overcome such problems. For example, Inspired by sea urchins, combination of soft suction

pad and chemical adhesive material improve the grasping on very rough surfaces ([14]). [15] microfabricated a

thin elastomer with multiple micro-suction cups in an octopus-like suction cup. Furthermore, [16], Developed

a micro-bumps surface for rough surface grasping. Aside from the bio-inspired designs, [17] designed a ﬁlmed

base suction cup that can attach to rough and porous surfaces.

Another challenge for vacuum suction cups is grasping objects with unknown-shaped objects and angular

surfaces. The suction cups require ﬂexibility to adapt to the object’s surface to overcome this issue. [18] suggest

attaching a thin elastomer membrane to the suction cup, enabling it to attach to round objects. [19] proposed

an origami-based design to adjust to the object’s shape by actuating shape memory alloys. Finally, inspired by

Octopus, [20] attached the suction cups to a ﬂexible stalk to emulate spherical joint behavior.

Although each design solves a critical problem, most of them pay the most attention to grabbing an object rather

than attaching it to an angular surface, which can beneﬁt applications such as manipulating unknown objects.

Furthermore, the ﬂexibility in these designs that makes the adaptation possible causes a lack of stiﬀness, which

can be problematic for manipulation applications. Several researchers have investigated methods to tackle this

paucity using stiﬀness modulation techniques, such as employing layer jamming to increase and control the

vertical stiﬀness, enabling lifting heavier objects [21]. In addition, [22] designed a cloth-rubber beam to provide

enough stiﬀness for surgical applications. Also, in the origami design of [19], the shape memory alloys endow

the design with the possibility to lift 50 times more of its weight. However, most studies do not discuss bending

stiﬀness, which plays a signiﬁcant role in wall-climbing applications.

In nature, octopus suction cups provide the best solution for adaptation and bending stiﬀness. Octopus, similar

to other Cephalopod mollusks, such as squids and cuttleﬁsh, employ muscular hydrostats which make them

capable of active stiﬀening and force generation [23][24]. In the suction cup, the octopus uses muscular

hydrostats to not only adapt the surface and generate the negative pressure required for grasping but also control

the bending stiﬀness and manipulate the grasped object using the extrinsic muscle of the suction cup. The

extrinsic muscle is the muscle that connects the sphincter to the arm of the octopus.

In this study, we propose a new granular jamming base suction cup inspired by the rotary behavior of octopus

suction cups [20][24] and jamming designs [25] [26]. This design adapts steep angular surfaces with the

material’s compliance and provides high bending stiﬀness after the attachment with the vacuum of granular

particles. The stiﬀness modulation in this design does not require an additional actuator, which helps weight

and energy eﬃciency. In addition, the design is sensorless and simpliﬁes the control in many applications. This

study investigated how changing parameters such as pressure, angle, and material compliance aﬀect the design

performance.

2 Material and Methods

2.1 Design and Fabrication

Figure 1: (A) Schematic drawing of octopus suction cup and the connection to arm via extrinsic muscle.

The extrinsic muscle enable the octopus suction cup to have rotary manipulation and also provide stiﬀness

modulation. (B) Drawing of the proposed suction cup. (C) The adaptation sequence of the suction cup to a

angular surface.

In the design shown in Fig 1, a soft stalk is attached to a conventional suction pad to imitate wrist-like behavior

for passive adaptation to angular surfaces. Although in this design, the ﬂexibility of compliant materials renders

the possibility of adaptation to steep angles, the low stiﬀness of such materials reduces the bending tolerance

which can be disadvantageous in some applications such as wall-climbing and grasping object from lateral

side. Therefore, stiﬀness modulation techniques endow this design with high ﬂexibility of compliant materials

for adaptation and high shear resistance after surface attachment. We choose granular jamming as a stiﬀness

modulation method, since it can be activated by negative pressure. This creates the possibility to use the same

source of negative pressure for activation of both suction cup and stiﬀness tunable stalk. This stalk design

perform similar to octopus extrinsic muscle which enables angular manipulation and adaptation for the suction

cup.

For fabrication of the suction pad, we degassed silicone rubber (1atm, degassing time: 10min) and poured it into

a 3D-printed mold. For the experiments, series of suction cups were fabricated with diﬀerent silicone rubbers

(Ecoﬂex 00-10 and Dragonskin 10, Smooth ON) to study how the suction pad softness aﬀects the adaptation.

In the fabrication of the soft stalk, as presented in Fig2, we cast a thin ﬁlm of Ecoﬂex 00-10 with a thickness of

0.2 mm on a plate using the doctor blade casting method [27] and cured it in the oven (60◦). Using such a thin

ﬁlm makes the design signiﬁcantly compliant during adaptation and stiﬀ after attachment. After the silicon was

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摘要：

ABioinspiredStinessTunableSuckerforPassiveAdaptationandFirmAttachmenttoAngularSubstratesArmanGoshtasbiDepartmentofBiomechanicalEngineeringUniversityofTwenteEnschede,TheNetherlandsa.goshtasbi@student.utwente.nlAliSadeghiDepartmentofBiomechanicalEngineeringUniversityofTwenteEnschede,TheNetherlandsa.s...

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ABioinspiredStiﬀnessTunableSuckerforPassiveAdaptationandFirm Attachment to Angular Substrates Arman Goshtasbi

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