Modeling, Design, and Implementation of an Underactuated Gripper with Capability of Grasping Thin Objects

Underactuated robotic grippers have the advantage of lower cost, simpler control, and higher safety over the fully actuated grippers. In this study, an underactuated robotic finger is presented. The design issues that should be considered for stable grasping are discussed in detail. This robotic finger is applied to design a two-fingered underactuated gripper. Firstly, a new three-DOF linkage-driven robotic finger that combines a five-bar mechanism and a double parallelogram is presented. This special architecture allows us to put all of the required actuators into the palm. By adding a torsion spring and a mechanical stopper at a passive joint, this underactuated finger mechanism can be used to perform parallel grasping, shape-adaptive grasping, and environmental contact-based grasp. Secondly, the dynamic model of this robotic finger is developed to investigate how to select an appropriate torsion spring. The dynamic simulation is performed with a multi-body dynamic simulator to verify our proposed approach. Moreover, static grasp models of both two-point and three-point contact grasps are investigated. Finally, different types of grasping modes are verified experimentally with a two-fingered underactuated robotic gripper.

Comparison of under-actuated and fully-actuated serial robotic arms: a case study

Under-actuated robots are very interesting in terms of cost and weight since they can result in a state-controllable system with a number of actuators lower than the number of joints. In this paper, a comparison between an under-actuated planar 3 degrees of freedom (DOF) robot and a comparable fully-actuated 2 degrees of freedom robot is presented, mainly focusing on the performances in terms of trajectories, actuator torques, and vibrations. The under-actuated system is composed of 2 active rotational joints followed by a passive rotational joint equipped with a torsional spring. The fully-actuated robot is inertial equivalent to the under-actuated manipulator: the last link is equal to the sum of the last two links of the under-actuated system. Due to the conditions on the inertia distribution and spring placement, in a simple point-to-point movement the last passive joint starts and ends in a zero-value configuration, so the 3 DOF robot is equivalent, in terms of initial and final configuration, to the 2 DOF fully-actuated robot, thus they can be compared. Results show how while the fully actuated robot is better in terms of reliable trajectory and actuator torques, the under-actuated robot wins in flexibility and vibration behavior.

Acute Effects of Dermal Suction on Passive Muscle and Joint Stiffness

The aim of the present study was to examine the acute effects of dermal suction on the passive mechanical properties of specific muscles and joints. Dermal suction was applied to the calves of 24 subjects. Passive plantar flexion torque was measured with the right knee fully extended and the right ankle positioned at 20°, 10°, 0°, and −10° angles, where 0° represents the ankle neutral position, and positive values correspond to the plantar flexion angle. The shear wave velocity (SWV) (m/s) of the medial gastrocnemius was measured in the same position using ultrasound shear wave elastography. The relationship between the joint angle and passive torque at each 10° angle was defined as passive joint stiffness (Nm/°). Passive muscle and joint stiffness were measured immediately before and after the dermal suction protocol. When the ankle joint was positioned at 20° (r = 0.53, P = 0.006), 10° (r = 0.43, P = 0.030), and −10° (r = 0.60, P = 0.001), the SWV was significantly higher after dermal suction than that before dermal suction. Regarding joint stiffness, we found no significant difference between the pre- and post-dermal suction values (partial η2 = 0.093, P > 0.05). These findings suggest that dermal suction increases passive muscle stiffness and has a limited impact on passive joint stiffness.

Vibrations and spasticity

This experimental study aims to evaluate and validate the effectiveness of the proposed application method in the use of "focused mechanical vibrations" for the treatment of muscle spasticity. The basic concept of this study is that in spasticity, by specifically stimulating some clearly identifiable trigger points of the body, better results are obtained; in fact, with the localized mechanical-sound vibrations, by positioning the handpiece for the treatment on those specific points, immediate generalized relaxation of the entire spastic muscle is obtained through reflex pathways. To evaluate this operative reality we treated 5 subjects affected by neurological pathology with spasticity and at T0 time (before treatment) and at T1 time (immediately after treatment), they were assessed with Ashworth Scale, Passive joint evaluation, Evaluation of active motility, Test of Bahkta (for non-functioning hand), surface electromyography The subjects were treated with a 120Hz vibratory therapy handpiece for a total time of 15 minutes The data showed us a clear improvement of the parameters lost in the exam, in the less serious patients and a good improvement also in the most serious subjects.

Father-child dyads exhibit unique inter-subject synchronisation during co-viewing of animation video stimuli

ABSTRACTInter-subject synchronisation reflects the entrainment of two individuals to each other’s brain signals during passive joint tasks. Within the parent-child dyad, the temporal coordination of signals indicates an attunement to each other’s emotional states. Despite the ubiquity with which parents and their children watch screen media together, no study has investigated intersubject synchronisation in father-child dyads during such a co-viewing activity. The present study examined whether father-child dyads would exhibit unique inter-subject synchronisation during co-viewing of narrative visual scenes that is unique to the dyad and hence would not be observed in control dyads (i.e. randomly paired signals). Hyperscanning fNIRS was used to record the prefrontal cortex (PFC) signals of 29 fathers and their preschool-aged children (11 girls, 18 boys) as each pair engaged in a typical activity of watching children’s shows together. Three 1-min video clips from “Brave”, “Peppa Pig” and “The Incredibles” were presented to each dyad and children’s ratings of video positivity and familiarity were obtained afterwards. PFC activity was analysed according to four clusters: medial left, medial right, frontal left and frontal right clusters. Results from synchrony analyses demonstrated that true father-child dyads showed significantly greater inter-subject synchronisation than control dyads, especially in the medial left cluster during the emotionally arousing conflict scene. Dyads with older fathers displayed less synchrony and older fathers, compared to younger ones, were also found to exhibit greater activity in the frontal right cluster. These findings point to a unique inter-subject synchronisation that exists in father-child relationships during shared co-viewing of narrative scenes which could be potentially modulated by parental age.