Macrobend optical sensing for pose measurement in soft robot arms

Abstract

This paper introduces a pose sensing system for soft robot arms integrating a set of macrobend stretch sensors. The macrobend sensory design in this study consists of optical fibres and is based on the notion that bending an optical fibre modulates the intensity of the light transmitted through the fibre.This sensing method is capable of measuring bending, elongation and compression in soft continuum robots and is also applicable to wearable sensing technologies, e.g. pose sensing in the wrist joint of a human hand. In our arrangement, applied to a cylindrical soft robot arm, the optical fibres for macrobend sensing originate from the base, extend to the tip of the arm, and then loop back to the base. The connectors that link the fibres to the necessary opto-electronics are all placed at the base of the arm, resulting in a simplified overall design.The ability of this custom macrobend stretch sensor to flexibly adapt its configuration allows preserving the inherent softness and compliance of the robot which it is installed on. The macrobend sensing system is immune to electrical noise and magnetic fields, is safe (because no electricity is needed at the sensing site), and is suitable for modular implementation in multi-link soft continuum robotic arms.The measurable light outputs of the proposed stretch sensor vary due to bend-induced light attenuation (macrobend loss), which is a function of the fibre bend radius as well as the number of repeated turns. The experimental study conducted as part of this research revealed that the chosen bend radius has a far greater impact on the measured light intensity values than the number of turns (if greater than five). Taking into account that the bend radius is the only significantly influencing design parameter, the macrobend stretch sensors were developed to create a practical solution to the pose sensing in soft continuum robot arms. Henceforward, the proposed sensing design was benchmarked against an electromagnetic tracking system (NDI Aurora) for validation.

Anchoring like octopus: biologically inspired soft artificial sucker

“…The diffuse-reflective fiber optic systems [37][38][39][40], which exploit the light intensity modulation sensing principle [37][38][39][40][41][42][43], can potentially provide better opportunities for seamless measurement of tactile and proximity information in practical applications. The non-contact nature of the sensing principle enables performing the measurements independent of the geometry of the embodying structure and the actuation system and, hence, no action is required for transition between the two modes of sensing.…”

“…The fiber optic sensors are free of electrical current in the sensing site making them inherently safe for integration into anchoring modules that can potentially be attached to vulnerable substrates or human body. Moreover, they are suitable for integration into soft robotic systems; since the flexibility of optical fiber can preserve the inherent softness of this class of robots [39][40][41].…”

“…for a physical load of 1.09 N (note that the swing of the anchoring module about the anchor point increases the distance between the optical fiber tip and the contact surface, and hence, reduces the sensor signal). The repeatability of the sensing values is defined as [41], Repeatability = (100 − standard deviation in repeated measurements sensing range ) % (4) and is calculated for the anchor length (across 5 actuation cycles under reverse sawtooth signal) as 93.7 %. The standards deviation is computed in MATLAB as 0.56 mm and the tactile sensing range is set to 9 mm.…”

An Inductance-Based Sensing System for Bellows-Driven Continuum Joints in Soft Robots

“…Strain can also be measured using elastomers with elements that exhibit changes in resistance or capacitance [2,24,26]. Optical fibers can measure strain (and thus bending) via Fiber Bragg Gratings [17] or deformation-induced attenuation [25]. Elastomeric waveguides can also be used [32,28].…”

A Multi-Modal Sensing Glove for Human Manual-Interaction Studies

“…Visual-based HPR systems, such as the ones described in [1,2,6], are quite accurate, inexpensive and unobtrusive, but they are not suitable for ambulatory monitoring during daily life activities. In contrast, glove-based HPR devices, relying on off-the-shelf flex sensors [3,10], dielectric elastomer stretch sensors [11], optical fibers [12], or inertial measurement units [4], are intrinsically ambulatory, but they are often less usable than visual-based systems due to obtrusive wiring and rigid sensor technology that does not adapt to the dynamically changing hand shape of the users. Indeed, the human body, and the human hand in particular, have a high number of degrees of freedom (DOFs) that act on a continuously compliant structure.…”