Stiffness Imaging With a Continuum Appendage: Real-Time Shape and Tip Force Estimation From Base Load Readings

Abstract

In this paper, we propose benefiting from load readings at the base of a continuum appendage for real-time forward integration of Cosserat rod model with application in configuration and tip load estimation. The application of this method is successfully tested for stiffness imaging of a soft tissue, using a 3-DOF hydraulically actuated braided continuum appendage. Multiple probing runs with different actuation pressures are used for mapping the tissue surface shape and directional linear stiffness, as well as detecting non-homogeneous regions, e.g. a hard nodule embedded in a soft silicon tissue phantom. Readings from a 6-axis force sensor at the tip is used for comparison and verification. As a result, the tip force is estimated with 0.016-0.037 N (7-20%) mean error in the probing and 0.02-0.1 N (6-12%) in the indentation direction, 0.17 mm (14%) mean error is achieved in estimating the surface profile, and 3.4-15 [N/m] (10-16%) mean error is observed in evaluating tissue directional stiffness, depending on the appendage actuation. We observed that if the appendage bends against the slider motion (toward the probing direction), it provides better horizontal stiffness estimation and better estimation in the perpendicular direction is achieved when it bends toward the slider motion (against the probing direction). In comparison with a rigid probe, ≈ 10 times smaller stiffness and ≈ 7 times larger mean standard deviation values were observed, suggesting the importance of a probe stiffness in estimation the tissue stiffness.

Data–Driven Disturbance Observers for Estimating External Forces on Soft Robots

“…It is worth underscoring that in this paper we are interested in capturing low frequency contact information, and we do not claim that our method is appropriate for instantaneous reaction to contact events [13]. Still, important possible applications enabled by our method include kinesthetic teaching [16], mapping environment geometry through touch [17], and environmental stiffness sensing [18].…”

Conditioned haptic perception for 3D localization of nodules in soft tissue palpation with a variable stiffness probe

“…In this study, we highlighted the importance of tuning the stiffness of a compliant palpation probe to shape the force peak prominence likelihood during a palpation task, and we proposed a controller that utilizes this principle to estimate the 3D localization of a nodule. This study highlights the role of compliance of a soft robot not only as a design parameter for safety but also as a control parameter for improved haptic perception [54].…”

FBG-Based Estimation of External Forces Along Flexible Instrument Bodies

“…The problem of estimating externally applied forces on robotic manipulators is not new. There has been an abundance of works carried out on rigid link robots (Jung et al, 2006;Colome et al, 2013;Daly and Wang, 2014;Hu and Xiong, 2018), and more recently, on soft/continuum robots (Yasin and Simaan, 2020;Sadati et al, 2020;Xu and Simaan, 2010;Gao et al, 2020). Regarding the latter, most of the previous works focused on estimating the contact force at the tip of the manipulator/instrument, rather than along the whole body.…”

“…Hooshiar et al estimate tip forces by employing Bezier spline shape approximations and an inverse Cosserat rod model (Hooshiar et al, 2020). Sadati et al employed force sensor readings at the base of a continuum appendage and the Cosserat rod model for tip load estimation (Sadati et al, 2020). Further examples of previous works on tip force estimation using kinematic models can be found in (Khoshnam et al, 2015;Khan et al, 2017).…”