A Spring-Based Inductive Sensor for Soft and Flexible Robots

Abstract

The development of flexible and soft robots generates new needs in terms of instrumentation, as large encountered deformations require highly stretchable strain sensors. In this regard, we contribute to the adoption of inductive sensors by providing tools to model and exploit them, and showing their relevance experimentally. First, strain estimation based on voltage measurement is proposed. Compared to direct inductance evaluation, the principle is easier to implement and opens the possibility to optimize the measurement performances by tuning the circuit components and interrogation frequency. The possibility of performing a single sensor calibration independently via the elongation mode during strain sensing is outlined. A detailed characterization is then performed which shows that the sensor produces a low hysteresis of 0.1 %, a precision in the order of 0.14 %, and an accuracy of 0.9 %. Finally, two proofs of concept are proposed: I) The integration with a pneumatic artificial muscle (PAM) that demonstrates the added value of the sensor for a model-free precise control of a soft system; II) The closed-loop control of a flexible bending manipulator using the inductive sensor. The performance in the closed-loop control is demonstrated, with a sensing element that is easy to integrate mechanically, strengthening its potential to be used as a structural element as well.

Stretchable and Highly Sensitive Flexible Strain Sensor Based on a Three‐Layer Core–Shell Structure of Polydopamine/Polypyrrole@Natural Rubber for Human Activity Monitoring

“…They have potential applications in the fields of human health monitoring, [5][6][7] smart textiles, [8][9][10] electronic skin, [11,12] soft robotics, [13] and so forth. Compared to traditional sensors, flexible strain sensors have excellent flexibility, portability, and stretchability.…”

End-Point Position Estimation of a Soft Continuum Manipulator Using Embedded Linear Magnetic Encoders

“…A root mean square (RMS) error of ° regarding the orientation of a single module is reported, together with a 1.3 mm error for a lateral displacement of 14 mm when a perpendicular external load is applied at the distal end. Other concepts based on the variable inductance of coils or helical springs have been proposed in [ 13 , 14 , 15 ]. In [ 15 ], a helical spring sensor is used on a continuum robot with 140 mm length and 20 mm diameter actuated in bending only.…”

“…Other concepts based on the variable inductance of coils or helical springs have been proposed in [ 13 , 14 , 15 ]. In [ 15 ], a helical spring sensor is used on a continuum robot with 140 mm length and 20 mm diameter actuated in bending only. A mean error of 5 mm in the desired radius of curvature is reported using open loop control, and is reduced to 2 mm when using closed loop control.…”

Recent developments in stretchable and flexible tactile sensors towards piezoresistive systems: A review

“…These sensors are designed to measure pressure, force, strain, bend, or twist in different applications, such as healthcare, 22,23 human motion detection, [24][25][26] human-robot interaction, 27,28 automation, 29,30 and soft robotics. [31][32][33] The stretchable and flexible sensors have an advantage in closeness to the human skin, softness, stretching, flexibility, and adaptability to complex surfaces; in some cases, even pigmentation has been provided to the elastomer material. [34][35][36] The development of artificial skin is enrooted in the development of stretchable and flexible sensors.…”

“…They are fabricated using stretchable and flexible materials, allowing them to be deformed or bent without breaking or losing their ability to function. These sensors are designed to measure pressure, force, strain, bend, or twist in different applications, such as healthcare, 22,23 human motion detection, 24–26 human‐robot interaction, 27,28 automation, 29,30 and soft robotics 31–33 . The stretchable and flexible sensors have an advantage in closeness to the human skin, softness, stretching, flexibility, and adaptability to complex surfaces; in some cases, even pigmentation has been provided to the elastomer material 34–36 .…”