Soft curvature sensors for measuring the rotational angles of mechanical fingers

doi:10.1007/s11465-020-0596-0

Front. Mech. Eng.

2020, Vol. 15

Issue (4) : 610-621 https://doi.org/10.1007/s11465-020-0596-0

RESEARCH ARTICLE

Soft curvature sensors for measuring the rotational angles of mechanical fingers

Haixiao LIU, Li LI(

), Zhikang OUYANG, Wei SUN

School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200444, China

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Abstract

The design, fabrication, and testing of soft sensors that measure elastomer curvature and mechanical finger bending are described in this study. The base of the soft sensors is polydimethylsiloxane (PDMS), which is a translucent elastomer. The main body of the soft sensors consists of three layers of silicone rubber plate, and the sensing element is a microchannel filled with gallium-indium-tin (Ga-In-Sn) alloy, which is embedded in the elastomer. First, the working principle of soft sensors is investigated, and their structure is designed. Second, the relationship between curvature and resistance is determined. Third, several sensors with different specifications are built in accordance with the structural design. Experiments show that the sensors exhibit high accuracy when the curvature changes within a certain range. Lastly, the soft sensors are applied to the measurement of mechanical finger bending. Experiments show that soft curvature sensors can effectively reflect mechanical finger bending and can be used to measure the bending of mechanical fingers with high sensitivity within a certain working range.

Keywords soft sensor Ga-In-Sn alloy strain sensing curvature sensing mechanical finger bending

Corresponding Author(s): Li LI

Just Accepted Date: 08 September 2020 Online First Date: 28 September 2020 Issue Date: 02 December 2020

Cite this article:

Haixiao LIU,Li LI,Zhikang OUYANG, et al. Soft curvature sensors for measuring the rotational angles of mechanical fingers[J]. Front. Mech. Eng., 2020, 15(4): 610-621.

URL:

https://academic.hep.com.cn/fme/EN/10.1007/s11465-020-0596-0
https://academic.hep.com.cn/fme/EN/Y2020/V15/I4/610

Material type	Material	Resistivity/(W·m)	Detection mode	Reference
Solid metal	Constantan foils	$4.80 × 10 – 7$ (typical)	DC	[¹⁵]
Liquid metal	Liquid-phase Ga-In alloy	$2.94 × 10 – 7$ (typical)	DC	[¹⁶,¹⁷]
Liquid metal	Ga-In-Sn	$2.89 × 10 – 7$ (typical)	DC	Method proposed in this study
Ionic liquid	1-ethyl-3-methylimidazolium bis	$2.40 × 10 – 4$ (typical)	AC	[¹⁹,²⁰]
Ionic liquid	KI-Gly	$7.40$ (typical)	AC	[²¹]

Tab.1 Comparison of different conductor materials

Fig.1 Schematic of elastomer bending.

Fig.2 Comparison of the structural design of serpentine and linear microchannels.

Fig.3 Aerial view of the soft curvature sensors.

Fig.4 Production of a soft curvature sensor.

Fig.5 Experimental platform for the stretching of a soft curvature sensor.

Fig.6 Resistance change in the soft curvature sensor when stretched by 10 mm (strain: 11.2%).

Fig.7 Resistance performance under different stretching lengths for repeated experiments: (a) Stretched by 10, 20, and 30 mm; (b) comparison of the stretched sensor.

Fig.8 Resistance performance of the soft curvature sensor under loading and unloading conditions.

Fig.9 Experimental platform for measuring mechanical fingers with the soft curvature sensor: (a) Experimental platform, (b) large bending angle, and (c) small bending angle.

Fig.10 Diagram of a mechanical index finger.

Fig.11 Performance of the soft curvature sensor when the mechanical finger rotates.

Fig.12 Distribution of resistance changes of the soft curvature sensor versus the rotational angle of the mechanical finger: (a) Global curve; curve segments of (b) A, (c) B, and (d) C noted in (a).

Fig.13 Histogram of the deviation between theoretical and experimental

Δ R

Fig.14 Comparison of the measured rotational angle and theoretical values for repeated experiments.

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