An inductance-based sensing system for bellows-driven continuum joints in soft robots

Abstract

In this work we present a novel, inductance-based system to measure and control the motion of bellows-driven continuum joints in soft robots. The sensing system relies on coils of wire wrapped around the minor diameters of each bellows on the joint. As the bellows extend, these coils of wire become more distant, decreasing their mutual inductance. Measuring this change in mutual inductance allows us to measure the motion of the joint. By dividing the sensing of the joint into two sections and measuring the motion of each section independently, we are able to measure the overall deformation of the joint with a piece-wise constant-curvature approximation. This technique allows us to measure lateral displacements that would be otherwise unobservable. When measuring bending, the inductance sensors measured the joint orientation with an RMS error of 1.1 °. The inductance sensors were also successfully used as feedback to control the orientation of Correspondence to: Wyatt Felt. Disclosure of potential conflicts of interest. Authors Wyatt Felt and C. David Remy are listed as inventors on a patent application for inductance sensing on bellows actuators. The other authors are (or were) employed by Pneubotics and/or its parent organization, Otherlab. Each of them has an investment interest with the company, and each is listed as an inventor in patents related to this work.

Foundations for Soft, Smart Matter by Active Mechanical Metamaterials

“…For robust, self‐sensing soft robots, an inductance‐based system was presented in ref. [ 177 ] and demonstrated improved joint deformation monitoring of a bellows‐driven soft robot than those with traditional inertial measurement units.…”

Improved Continuum Joint Configuration Estimation Using a Linear Combination of Length Measurements and Optimization of Sensor Placement

“…Other physical phenomenon used include capacitance (Yuen et al, 2017 , 2018 ; Bilodeau et al, 2018 ; Case et al, 2018 ), inductance (Felt et al, 2016 , 2018 , 2019 ), magnetism (Ozel et al, 2016 ), impedance (Avery et al, 2019 ), or a combination of gyroscope, accelerometer, and magnetometer in an inertial measurement unit (IMU) package (Hyatt et al, 2019 ).…”

“…Specifically, Li et al ( 2020 ) used a dual array FBG scheme to improve estimation accuracy. While Felt et al ( 2019 ) used two circuits and measured change in inductance to improve estimation of lateral motion for a continuum joint.…”

Design Considerations for 3D Printed, Soft, Multimaterial Resistive Sensors for Soft Robotics

“…al. designed an inductance-based sensing system to measure and control bellowed continuum joints, by wrapping coils of wires and measuring changes in inductance (Felt et al, 2017 ). We (Shih et al, 2017 ) and others (Bilodeau et al, 2015 ; Farrow and Correll, 2015 ), have embedded soft sensors for measuring bending into the layers of pneumatic fingers, which enabled the fingers to estimate the shapes of various objects using tactile sensing (Bilodeau et al, 2015 ; Farrow and Correll, 2015 ; Zhao et al, 2016 ; Shih et al, 2017 ).…”