Stefano Seriani

A Performance Index for Planar Repetitive Workspace Robots

When large surfaces need to be covered by a robotic system, the most common solution is to design or employ a robot with a comparably large workspace (WS), with high costs and high power requirements. In this paper, we propose a new methodology consisting in an efficient partitioning of the surface, in order to use robotic systems with a workspace of arbitrarily smaller size. These robots are called repetitive workspace robots (RWR). To support this method, we formally define a general index IRWR in order to evaluate the covering efficiency of the workspace. Three algorithms to compute the index are presented, the uniform expansion covering algorithm (UECA), the corrected inertial ellipsoid covering algorithm (CIECA), and the genetic covering algorithm (GCA). The GCA, which delivers a solution in the proximity of the global-best one, is used as a baseline for a comparison between the UECA and the CIECA. Eventually, we present the results of a performance analysis of the three algorithms in terms of computing time. The results show that the CIECA is the best algorithm for the evaluation of the IRWR, almost reaching the global-best solutions of the GCA. Finally, we illustrate a practical application with a comparison between two commercial industrial paint robots: the ABB™ IRB 550 and the CMA® Robotics GR 6100.

The cell-stretcher: A novel device for the mechanical stimulation of cell populations

Mechanical stimulation appears to be a critical modulator for many aspects of biology, both of living tissue and cells. The cell-stretcher, a novel device for the mechanical uniaxial stimulation of populations of cells, is described. The system is based on a variable stroke cam-lever-tappet mechanism which allows the delivery of cyclic stimuli with frequencies of up to 10 Hz and deformation between 1% and 20%. The kinematics is presented and a simulation of the dynamics of the system is shown, in order to compute the contact forces in the mechanism. The cells, following cultivation and preparation, are plated on an ad hoc polydimethylsiloxane membrane which is then loaded on the clamps of the cell-stretcher via force-adjustable magnetic couplings. In order to show the viability of the experimentation and biocompatibility of the cell-stretcher, a set of two in vitro tests were performed. Human epithelial carcinoma cell line A431 and Adult Mouse Ventricular Fibroblasts (AMVFs) from a dual reporter mouse were subject to 0.5 Hz, 24 h cyclic stretching at 15% strain, and to 48 h stimulation at 0.5 Hz and 15% strain, respectively. Visual analysis was performed on A431, showing definite morphological changes in the form of cellular extroflections in the direction of stimulation compared to an unstimulated control. A cytometric analysis was performed on the AMVF population. Results show a post-stimulation live-dead ratio deviance of less than 6% compared to control, which proves that the environment created by the cell-stretcher is suitable for in vitro experimentation.

Variable Radius Drum Mechanisms

This paper presents the concept of variable radius drum mechanisms (VRDMs). A drum, or spool, consists of a spindle with flanges, around which a cable is wound. The cylindrical surface of an ordinary spool has a constant radius. In a variable radius drum (VRD), the radius of the spool varies along its profile. Properties of such devices are discussed, as well as the kinematic analysis and synthesis. The main contribution of the work is the theory of the VRD synthesis problem, rooted in a closed-form analytical solution. In order to highlight the benefits of VRDMs, two applications are presented and analyzed as examples. The first example consists of a mechanism which can support and guide a load along a horizontal linear path. The second example shows a solution to improve the locomotion of a legged robot. Finally, a prototype is made on the basis of the first case scenario and its performance is evaluated and discussed, showing a remarkable accuracy, with a deviation from the nominal trajectory of less than 1%.

Dynamics of a Tethered Rover on Rough Terrain

The deployment of a complex modular cable robot is investigated. The act is performed by a supporting rover that drives on rough terrain while pulling—and unwinding—one of the tethers. In order to avoid rebounds and stress spikes, the cable must be kept in tension by the feeding mechanism. In this work, a constant torque control system is evaluated. A numerical simulation is carried out by direct time-integration of the dynamics equation of the cable and the drive. Results show that a constant torque applied by the motor unit is able to produce a tension in the cable that is well within the cable’s yield limits, while at the same time being consistently larger than zero. This shows the viability of this technology for the deployment of cable structures by rovers in extreme environments.

Task-Dependent Structural Modifications on Reconfigurable General Serial Manipulators

The monolithic design of serial robot arms has become widely accepted in industrial applications. One might note that these manipulators are designed in such a way that they can implement as many applications as possible at the same time and therefore do usually not have an application-specific structure. In this article we describe the construction and modeling of a kinematic chain in which a mechanical modification is possible. As a result, the structure of a serial robot can be adapted in a wide range. For this purpose, the links of the kinematic chain are modified in such a way that the robot structure matches the desired Denavit-Hartenberg parameter set. This means also that optimizations with different kinematic goals can be realized in order to flexibly adapt the robot system to a current task.

Experimental Evaluation of Vibrotactile Training Mappings for Dual-Joystick Directional Guidance

Two joystick-based teleoperation is a common method for controlling a remote machine or a robot. Their use could be counter-intuitive and could require a heavy mental workload. The goal of this paper is to investigate whether vibrotactile prompts could be used to trigger dual-joystick responses quickly and intuitively, so to possibly employ them for training. In particular, we investigate the effects of: (1) stimuli delivered either on the palm or on the back of the hand, (2) with attractive and repulsive mappings, (3) with single and sequential stimuli. We find that 38 participants responded quicker and more accurately when stimuli were delivered on the back of the hand, preferred to move towards the vibration. Sequential stimuli led to intermediate responses in terms of speed and accuracy.

Deoxynivalenol induces structural alterations in epidermoid carcinoma cells A431 and impairs the response to biomechanical stimulation

Morphology together with the capability to respond to surrounding stimuli are key elements governing the spatial interaction of living cells with the environment. In this respect, biomechanical stimulation can trigger significant physiological cascades that can potentially modulate toxicity. Deoxynivalenol (DON, vomitoxin) is one of the most prevalent mycotoxins produced by Fusarium spp. and it was used to explore the delicate interaction between biomechanical stimulation and cytotoxicity in A431 cells. In fact, in addition of being a food contaminant, DON is a relevant toxin for several organ systems. The combination between biomechanical stimulation and the mycotoxin revealed how DON can impair crucial functions affecting cellular morphology, tubulin and lysosomes at concentrations even below those known to be cytotoxic in routine toxicity studies. Sub-toxic concentrations of DON (0.1–1 μM) impaired the capability of A431 cells to respond to a biomechanical stimulation that normally sustains trophic effects in these cells. Moreover, the effects of DON (0.1–10 μM) were partially modulated by the application of uniaxial stretching (0.5 Hz, 24 h, 15% deformation). Ultimately, proteomic analysis revealed the potential of DON to alter several proteins necessary for cell adhesion and cytoskeletal modulation suggesting a molecular link between biomechanics and the cytotoxic potential of the mycotoxin.

The sense of agency shapes body schema and peripersonal space

Body schema, a sensorimotor representation of the body used for planning and executing movements, is plastic because it extends by using a tool to reach far objects. Modifications of peripersonal space, i.e., a functional representation of reach space, usually co-occur with body schema changes. Here, we hypothesized that such plastic changes depend on the experience of controlling the course of events in space trough one’s own actions, i.e., the sense of agency. In two experiments, body schema and peripersonal space were assessed before and after the participants’ sense of agency over a virtual hand was manipulated. Body schema and peripersonal space enlarged or contracted depending on whether the virtual hand was presented in far space, or closer to the participants’ body than the real hand. These findings suggest that body schema and peripersonal space are affected by the dynamic mapping between intentional body movements and expected consequences in space.

Preloaded Structures for Space Exploration Vehicles

This paper is devoted to the design and simulation of a rover equipped with 4 preloaded structure legs. Space exploration vehicles (rovers) are employed for moving sensors, transporting planet samples and manipulating small modules. In order to perform such tasks with high accuracy, high mechanical stiffness frames are required. At the same time, a certain degree of compliance is required to mitigate mechanical stress caused by motion over a rough surface or in case of unexpected collisions. For this reasons, preloaded structures could represent a suitable solution. They present sharp stiff-to-compliant transitions at design-determined load thresholds. The paper describes the dynamic model of a single rover leg, the simulation of an impact event and the overall design of system.

Busker Robot: A Robotic Painting System for Rendering Images into Watercolour Artworks

In this paper we present Busker Robot, an innovative robotic painting system for rendering digital images into watercolour artworks. The installation is composed of a 6-degrees of freedom collaborative robot and a series of image processing and path planning algorithms. These non-photorealistic techniques elaborate a digital image into a sequence of trajectories that the robot reproduces on paper. Our painting machine is the first robotic system that uses watercolour technique for artistic rendering. The resulting artworks have been considered of interest by the public and the press in recent international fairs and exhibitions.