A Low-Cost Soft Coiled Sensor for Soft Robots

Abstract

Soft robots made from soft materials can closely emulate biological system using simple soft mechanical structures. Compared with traditional rigid-link robots, they are safe to work with humans and can adapt to confined environments. As a result, they are widely used for various robotic locomotions and manipulations. Nevertheless, for soft robots, being able to sense its state to enable closed-loop control using soft sensors remains a challenge. Existing sensors include external sensors such as camera systems, electromagnetic tracking systems, and internal sensors such as optical fibers, conductive liquid, and carbon black filled strips. In this paper, we investigate a new soft sensor made from low-cost conductive nylon sewing threads. By continuously inserting twists into a thread under some weight, coils can be formed to enable a coiled soft sensor. The resistance of the sensor varies with the change of length. The fabrication and experiments for this new coiled sensor is described in this paper. Embedding this sensor to a 3D printed soft manipulator demonstrates the sensing capability. Compared to existing soft sensors, the coiled sensor is low-cost, easy to fabricate, and can also be used as an actuator. It can be embedded to any soft robot to measure the deformation for closed-loop feedback control.

Kinematics Modeling of a Twisted and Coiled Polymer-Based Elastomer Soft Robot

“…Substantially, CCM is a rigid robotics model applied to soft robotics depending on purely geometric calculations based on CCA; however, this model totally ignores elastic deformation, the basic nature of soft robots. Moreover, calculation based purely on geometry can only lead to the conclusion that the robot or sensor length is linear to temperature [16], which does not match with the experimental results.…”

“…Thus, the net force and torque at the cross section can be calculated and be substitute into Eq. (16). To simplify the formulation, we define r = ρ + y 0 .…”

FE Analyses of Hyperelastic Solids under Large Bending: The Role of the Searle Parameter and Eulerian Slenderness

“…The bending moment distribution w.r.t. the beam axis is obtained as m x (s i ) = M 0 , then the radius of curvature and rotation of the longitudinal axis are achieved by using relations (6)- (9). Finally, the deformed configuration is determined by using Equations (10) and (11) (see Figure 4b).…”

“…The soft robots [1], i.e., robots based on extremely compliant components, are used to produce pneumatic robots [2], to simulate artificial systems [3], animals [4], human hands [5] and other gripper devices [6]. For these kinds of high-tech applications, the mechanical role of the external load is played by the light [7], humidity [8] or electricity [9] to drive motion.…”

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

“…Resistance-based sensing is often used with conductive material or fabrics that are assembled in a way such that the resistance of a circuit varies as the bend angle of the robot changes. Examples use methods ranging from commercial flex sensors (Ozel et al, 2016 ), to conductive thread (Cianchetti et al, 2012 ; Zhao and Abbas, 2016 ; Abbas and Zhao, 2017 ), or yarn (Wurdemann et al, 2015 ), to conductive silicone that is cut using principles from kirigami (Truby et al, 2020 ). There are multiple examples of this approach (see Gibbs and Asada, 2005 ; She et al, 2015 ; Elgeneidy et al, 2016 , 2018 ; Yuen et al, 2017 ; Zhou et al, 2020 ).…”