A Variable Stiffness Robotic Probe for Soft Tissue Palpation

During abdominal palpation diagnosis, a medical practitioner would change the stiffness of their fingers in order to improve the detection of hard nodules or abnormalities in soft tissue to maximize the haptic information gain via tendons. Our recent experiments using a controllable stiffness robotic probe representing a human finger also confirmed that such stiffness control in the finger can enhance the accuracy of detecting hard nodules in soft tissue. However, the limited range of stiffness achieved by the antagonistic springs variable stiffness joint subject to size constraints made it unsuitable for a wide range of physical examination scenarios spanning from breast to abdominal examination. In this letter, we present a new robotic probe based on a variable lever mechanism able to achieve stiffness ranging from 0.64 to 1.06 N ⋅m/rad that extends the maximum stiffness by around 16 times and the stiffness range by 33 times. This letter presents the mechanical model of the novel probe, the finite element simulation as well as experimental characterization of the stiffness response for lever actuation

Significance of the compliance of the joints on the dynamic slip resistance of a bioinspired hoof

Robust mechanisms for slip resistance are an open challenge in legged locomotion. Animals such as goats show impressive ability to resist slippage on cliffs. It is not fully known what attributes in their body determine this ability. Studying the slip resistance dynamics of the goat may offer insight toward the biologically inspired design of robotic hooves. This article tests how the embodiment of the hoof contributes to solving the problem of slip resistance. We ran numerical simulations and experiments using a passive robotic goat hoof for different compliance levels of its three joints. We established that compliant yaw and pitch and stiff roll can increase the energy required to slide the hoof by ≈ 20% compared to the baseline (stiff hoof). Compliant roll and pitch allow the robotic hoof to adapt to the irregularities of the terrain. This produces an antilock braking system-like behavior of the robotic hoof for slip resistance. Therefore, the pastern and coffin joints have a substantial effect on the slip resistance of the robotic hoof, while the fetlock joint has the lowest contribution. These shed insights into how robotic hooves can be used to autonomously improve slip resistance

A State-Dependent Damping Method to Reduce Collision Force and Its Variability

This paper investigates the effect of biologically inspired angle-dependent damping profile in a robotic joint primarily on the magnitude and the variability of the peak collision force. Joints such as the knee that experience collision forces are known to have an angle-dependent damping profile. In this paper, we have quantified and compared three damping profiles. Our numerical and experimental results show that the proposed hyperbolic angle-dependent damping profile can minimize both the magnitude and the variability of the peak collision force(average magnitude and variability reduction of 26% and 47% compared to the peak constant damping profile). Very often, the variability of the force across the collision between the robot and the environment cause uncertainty about the state variables of the robotic joint. We show that by increasing the slope of the proposed hyperbolic angle-dependent damping profile, we can also reduce the variability and the magnitude of post-collision peak displacement and peak velocity compared to those of constant damping profile. This was achieved while reducing the mean root square of power consumed by the robotic joint

Granular jamming based controllable organ design for abdominal palpation

Medical manikins play an essential role in the training process of physicians. Currently, most available simulators for abdominal palpation training do not contain controllable organs for dynamic simulations. In this paper, we present a soft robotics controllable liver that can simulate various liver diseases and symptoms for effective and realistic palpation training. The tumors in the liver model are designed based on granular jamming with positive pressure, which converts the fluid-like impalpable particles to a solid-like tumor state by applying low positive pressure on the membrane. Through inflation, the tumor size, liver stiffness, and liver size can be controlled from normal liver state to various abnormalities including enlarged liver, cirrhotic liver, and multiple cancerous and malignant tumors. Mechanical tests have been conducted in the study to evaluate the liver design and the role of positive pressure granular jamming in tumor simulations

A stiffness controllable multimodal whisker sensor follicle for texture comparison

Mammals like rats, who live in dark burrows, heav-ily depend on tactile perception obtained through the vibrissalsystem to move through gaps and to discriminate textures. Theorganization of a mammalian whisker follicle contains multiplesensory receptors and glands strategically organized to capturetactile sensory stimuli of different frequencies. In this paper, weused a controllable stiffness soft robotic follicle to test the hy-pothesis that the multimodal sensory receptors together with thecontrollable stiffness tissues in the whisker follicle form a physicalstructure to maximize tactile information. In our design, the ringsinus and ringwulst of a biological follicle are represented by alinear actuator connected to a stiffness controllable mechanismin-between two different frequency-dependent data capturingmodules. In this paper, we show for the first time the effectof the interplay between the stiffness and the speed of whiskingon maximizing a difference metric for texture classification

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

This paper provides a solution for fast haptic information gain during soft tissue palpation using a Variable Lever Mechanism (VLM) probe. More specifically, we investigate the impact of stiffness variation of the probe to condition likelihood functions of the kinesthetic force and tactile sensors measurements during a palpation task for two sweeping directions. Using knowledge obtained from past probing trials or Finite Element (FE) simulations, we implemented this likelihood conditioning in an autonomous palpation control strategy. Based on a recursive Bayesian inferencing framework, this new control strategy adapts the sweeping direction and the stiffness of the probe to detect abnormal stiff inclusions in soft tissues. This original control strategy for compliant palpation probes shows a sub-millimeter accuracy for the 3D localization of the nodules in a soft tissue phantom as well as a 100% reliability detecting the existence of nodules in a soft phantom

Soft Fingertips with Tactile Sensing and Active Deformation for Robust Grasping of Delicate Objects

Soft fingertips have shown significant adaptability for grasping a wide range of object shapes thanks to elasticity. This ability can be enhanced to grasp soft, delicate objects by adding touch sensing. However, in these cases, the complete restraint and robustness of the grasps have proved to be challenging, as the exertion of additional forces on the fragile object can result in damage. This paper presents a novel soft fingertip design for delicate objects based on the concept of embedded air cavities, which allow the dual ability of adaptive sensing and active shape changing. The pressurized air cavities act as soft tactile sensors to control gripper position from internal pressure variation; and active fingertip deformation is achieved by applying positive pressure to these cavities, which then enable a delicate object to be kept securely in position, despite externally applied forces, by form closure. We demonstrate this improved grasping capability by comparing the displacement of grasped delicate objects exposed to high-speed motions. Results show that passive soft fingertips fail to restrain fragile objects at accelerations as low as 0.1m/s2 , in contrast, with the proposed fingertips, delicate objects are completely secure even at accelerations of more than 5m/s2