Research Papers

Design and Fabrication of a Soft Robotic Hand With Embedded Actuators and Sensors

[+] Author and Article Information
Yu She

Department of Mechanical and
Aerospace Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: she.22@osu.edu

Chang Li

Department of Mechanical Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: lichang427@sina.com

Jonathon Cleary

Department of Mechanical and
Aerospace Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: cleary.77@osu.edu

Hai-Jun Su

Department of Mechanical and
Aerospace Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: su.298@osu.edu

1Corresponding author.

Manuscript received August 17, 2014; final manuscript received December 23, 2014; published online February 27, 2015. Assoc. Editor: Aaron M. Dollar.

J. Mechanisms Robotics 7(2), 021007 (May 01, 2015) (9 pages) Paper No: JMR-14-1224; doi: 10.1115/1.4029497 History: Received August 17, 2014; Revised December 23, 2014; Online February 27, 2015

This paper details the design and fabrication process of a fully integrated soft humanoid robotic hand with five finger that integrate an embedded shape memory alloy (SMA) actuator and a piezoelectric transducer (PZT) flexure sensor. Several challenges including precise control of the SMA actuator, improving power efficiency, and reducing actuation current and response time have been addressed. First, a Ni-Ti SMA strip is pretrained to a circular shape. Second, it is wrapped with a Ni-Cr resistance wire that is coated with thermally conductive and electrically isolating material. This design significantly reduces actuation current, improves circuit efficiency, and hence reduces response time and increases power efficiency. Third, an antagonistic SMA strip is used to improve the shape recovery rate. Fourth, the SMA actuator, the recovery SMA strip, and a flexure sensor are inserted into a 3D printed mold which is filled with silicon rubber materials. The flexure sensor feeds back the finger shape for precise control. Fifth, a demolding process yields a fully integrated multifunctional soft robotic finger. We also fabricated a hand assembled with five fingers and a palm. We measured its performance and specifications with experiments. We demonstrated its capability of grasping various kinds of regular or irregular objects. The soft robotic hand is very robust and has a large compliance, which makes it ideal for use in an unstructured environment. It is inherently safe to human operators as it can withstand large impacts and unintended contacts without causing any injury to human operators or damage to the environment.

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Fig. 1

The conceptual design of the soft robotic hand

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Fig. 2

The actuation and shape recovery cycle of the SMA actuator: (a) initial position, (b) grasping position, and (c) releasing position

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Fig. 3

The schematic of the full integrated soft robotic finger

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Fig. 4

The overview of the fabrication process for the fully integrated robotic hand

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Fig. 5

Trained shape of the SMA strip

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Fig. 6

The coating and winding process of the SMA strip and the resistance wire

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Fig. 7

The 3D printed mold parts (left) and the complete assembled mold (right)

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Fig. 8

(a) The soft robotic finger body with various compliance. (b) The fabricated fully integrated soft robotic finger.

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Fig. 9

The bending process of the fully integrated soft robotic finger with an input current of 0.7 A at 7 V

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Fig. 10

The final radius of curvature ρ (mm) versus current I (A)

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Fig. 11

The response time to the full actuation t (s) versus the current I (A)

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Fig. 12

Comparison of the shape recovery process: without the recovery SMA actuator (circle) and with the recovery actuator (diamond)

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Fig. 13

Relation of resistance versus radius of the flexure sensor for forward and backward bending

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Fig. 14

PD control of the finger position with flexure sensor feedback

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Fig. 15

Grasping experiment of the assembled robot hand




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