This article focuses on haptic localization of very lightweight and delicate objects while applying a contact force >5000 times lower than the weight of the object. A soft whisker integrated with a Force/Moment (F/M) sensor at the base, and a novel reconstruction algorithm have been proposed for this purpose. Initially, the mathematical relationships between the deformations of the whisker and the F/M sensor outputs were used to reconstruct the shape of the whisker and the position of the touched object. The Cosserat rod theory was used under the assumption that only one contact point occurs during the exploration, and friction effects are negligible. A new methodology we called moment only reading (MOR) has been tested, verified, and compared with previous methods that employed Force and Moment Readings (FMR). Experimental investigations revealed that the spatial position estimation error of the MOR method was confined within 13 mm, when the force applied ranged between 0.001 and 0.01 N. Moreover, the comparison with FMR demonstrated that MOR is capable of retrieving the position of objects even when the force readings drop below the force resolution of the sensor. Eventually, the MOR method has been applied to demonstrate the localization and grasping, with a soft gripper, of delicate crops like tomatoes and strawberries.
Keywords: Cosserat rod theory; haptic localization; soft sensing; soft whisker.