Mexican-Hat-Like Response in a Flexible Tactile Sensor Using a Magnetorheological Elastomer

Abstract

A significant challenge in robotics is providing a sense of touch to robots. Even though several types of flexible tactile sensors have been proposed, they still have various technical issues such as a large amount of deformation that fractures the sensing elements, a poor maintainability and a deterioration in the sensitivity caused by the presence of a thick and soft covering. As one solution for these issues, we proposed a flexible tactile sensor composed of a magnet, magnetic transducer and dual-layer elastomer, which consists of a magnetorheological and nonmagnetic elastomer sheet. In this study, we first investigated the sensitivity of the sensor, which was found to be high (approximately 161 mV/N with a signal-to-noise ratio of 42.2 dB); however, the sensor has a speed-dependent hysteresis in its sensor response curve. Then, we investigated the spatial response and observed the following results: (1) the sensor response was a distorted Mexican-hat-like bipolar shape, namely a negative response area was observed around the positive response area; (2) the negative response area disappeared when we used a compressible sponge sheet instead of the incompressible nonmagnetic elastomer. We concluded that the characteristic negative response in the Mexican-hat-like response is derived from the incompressibility of the nonmagnetic elastomer.

Magnetic Polymer Composite Particles: Design and Magnetorheology

“…Ge et al [ 107 ] developed a displacement sensor by coating a porous MR elastomer with carbon nanotubes. A tactile sensor is another type of sensing device in the field of MR elastomers, Kawasetsu et al [ 108 ] developed a flexible tactile sensor based on an MR elastomer that could detect normal forces and vertical deformation in an application as given in Figure 10 c, and Lee et al [ 109 ] developed a micro-cantilever beam with MR elastomer characteristics. More recently, Xu et al [ 110 ] used an MR elastomer as a polishing composite material to perform magnetically controlled polishing.…”

“… Applications of ( a ) a finite element analysis model of a proposed MR brake (Patil et al [ 96 ], ©Elsevier Ltd., 2016), ( b ) a sectional view of an active damper based on an MR elastomer (Mikhailov et al [ 103 ], ©Elsevier B.V., 2016), and ( c ) the basic structure of a flexible tactile sensor (Kawasetsu et al [ 108 ], ©MDPI, 2018). …”

Geometry Optimisation of a Hall-Effect-Based Soft Fingertip for Estimating Orientation of Thin Rectangular Objects

“…The application of Hall-effect sensors was further investigated in the development of a distributed tactile sensor for measuring 3-axis forces [9]. A flexible tactile sensor that used a magnetorheological elastomer was introduced in [10] to address the issue of fractures and the poor maintainability of soft coverings. Solid magnets were replaced with a magnetic powder blended with silicone rubber to ensure force estimation without quick saturation and reduce the thickness of a sensing element [11].…”

Soft Magnetic Powdery Sensor for Tactile Sensing

“…Due to the nature of the detection principle, these capacitive sensors are susceptible to environmental noise. In contrast, magnetic tactile sensors measure applied force from changes in the magnetic field [12,13,14,15]. In this method, displacement and force are estimated by measuring the change in magnetic flux density caused by the change in position of the magnetic particles embedded in the material.…”