Luigi Biagiotti

Development of UB Hand 3: Early Results

The first part of this paper describes the development of a humanoid robot hand based on an endoskeleton made of rigid links connected with elastic hinges, actuated by sheath routed tendons and covered by continuous compliant pulps. The project is called UB Hand 3 (University of Bologna Hand, 3rd version) and aims to reduce the mechanical complexity of robotic end effectors yet maintaining full anthropomorphic aspect and a good level of dexterity. In the second part this paper focuses on the early experiences of the UB Hand 3 in performing manipulation tasks.

UBH 3: an anthropomorphic hand with simplified endo-skeletal structure and soft continuous fingerpads

The paper describes work in progress at the University of Bologna concerning the design of a new anthropomorphic robot hand. The hand is based on the modular assembly of articulated fingers that adopt an original configuration of their structure, made with rigid links connected by elastic hinges that are coaxially crossed by flexible tendons. This innovative design is suitable to host distributed sensory equipment and continuous compliant cover, allowing a high level of anthropomorphism together with great structural simplification, reliability enhancement and cost reduction. Furthermore, the proposed solution is very flexible, as it can be adapted to many different hand configurations and is not dependent on a particular type of actuation, being compatible with future availability of any kind of artificial muscles.

Cartesian impedance control for dexterous manipulation

In this work, a cartesian impedance controller purposely designed for dexterous manipulation is described. Based on the main features of the DLR Hand II, concerning kinematic structure and sensory equipment of fingers, this control strategy allows to overcome the main problems encountered in fine manipulation, namely: effects of the friction (and unmodeled dynamics) on robot performances and occurrence of singularity conditions. The achieved control scheme bas been experimentally validated by testing it on a finger of the DLR Hand.

Modelling and identification of soft pads for robotic hands

In this work the static and dynamic characterization of viscoelastic pads for robotic hands is performed. A quasi-linear model, developed to describe the behavior of human hand pads and, more generally, of biological tissues, is adopted in order to overcome the problems tied to classical (linear) models, often used in the robotic field. Through experimental tests, the values of the parameters of this model have been found for two different materials (a polyurethane gel and a silicon rubber) which show a behavior similar to that of human pads and seem very suitable for robotic applications. Finally, the model has been extended with the use of digital filters, making the identification process very straightforward.

An innovative stand-alone bioreactor for the highly reproducible transfer of cyclic mechanical stretch to stem cells cultured in a 3D scaffold

Much evidence in the literature demonstrates the effect of cyclic mechanical stretch in maintaining, or addressing, a muscle phenotype. Such results were obtained using several technical approaches, useful for the experimental collection of proofs of principle but probably unsuitable for application in clinical regenerative medicine. Here we aimed to design a reliable innovative bioreactor, acting as a stand‐alone cell culture incubator, easy to operate and effective in addressing mesenchymal stem cells (MSCs) seeded onto a 3D bioreabsorbable scaffold, towards a muscle phenotype via the transfer of a controlled and highly‐reproducible cyclic deformation. Electron microscopy, immunohistochemistry and biochemical analysis of the obtained pseudotissue constructs showed that cells ‘trained’ over 1 week: (a) displayed multilayer organization and invaded the 3D mesh of the scaffold; and (b) expressed typical markers of muscle cells. This effect was due only to physical stimulation of the cells, without the need of any other chemical or genetic manipulation. This device is thus proposed as a prototypal instrument to obtain pseudotissue constructs to test in cardiovascular regenerative medicine, using good manufacturing procedures. Copyright

Optimal Trajectories for Vibration Reduction Based on Exponential Filters

In this paper, a new type of trajectory, based on an exponential jerk, is presented along with filters for their online generation. The goal is to generalize constant jerk trajectories, widely used in industrial applications, in order to reduce vibrations of motion systems. As a matter of fact, constant jerk trajectories do not assure a complete vibration suppression when the damping of the resonant modes is not negligible. The values of the parameters (decay rate and duration) of the jerk impulses that allow residual vibration cancellation are derived in an analytical way as a function of the dynamic characteristics of the plant. Comparisons with the well-known input shaping techniques and with system-inversion-based filters show the advantages of the proposed method in terms of robustness with respect to modeling errors, smoothness of the resulting trajectory, and time duration of the motion under velocity and acceleration constraints.

B-spline based filters for multi-point trajectories planning

In this paper, the relation between B-splines and FIR (Finite Impulse Response) filters is demonstrated and exploited to design a digital filter for trajectory planning, combining the very simple structure and computational efficiency of FIR filters with the flexibility of splines. In particular, the trajectory generator consists of two main elements. The former is devoted to the solution of an optimization problem that, given a set of points to be interpolated (or approximated), provides the control points defining the spline. The latter, a cascade of moving average filters, gives the trajectory profile at each sampling time on the basis of such points. The proposed method has been applied to several robotic and industrial applications, and in this paper two case studies are reported as examples: an industrial robot performing a welding operation and a mobile robot moving in an environment with obstacles. With respect to these tasks, the main features of the trajectory generator are shown: the possibility of planning trajectories with high degree of smoothness (continuity of the derivatives), the possibility of easily changing the duration of the trajectory (and therefore the velocity, acceleration, jerk, etc. of the trajectory) maintaining the same geometric path, the possibility of locally modifying the pre-planned path.

Control of a robotic gripper for grasping objects in no-gravity conditions

In space applications, it is conceivable that part of the robotic activities could involve the grasp and/or manipulation of free-floating objects in the absence of gravity. In this case, synchronous application of contacts seems to represent a basic feature in order to efficiently grasp the floating items. In this sense, an additional difficulty is that objects may have irregular shape and/or be non well positioned in the gripper workspace. These difficulties cannot be handled in a simple way with standard 2-jaw grippers, with one (or two) degrees of freedom. In the paper, an activity for designing and experimenting with a gripper for this type of operations is reported, and the first laboratory results are presented and discussed. The main features of the gripper are its kinematic configuration (3 fingers with 3 dof) and its sensorial equipment, features that improve the dexterity of this device if compared to more classical devices.

Online trajectory planning and filtering for robotic applications via B-spline smoothing filters

In this paper, a novel technique for online generating trajectories in the 3-D space is presented. The trajectory planner is based on cubic B-splines. However, while the definition of B-splines requires the solution of a global problem that involves the entire set of via-points to be interpolated/approximated, and therefore it is not suitable for online implementation, the proposed generator is able to approximate spline functions with the prescribed precision on the basis of local computations, which only need the knowledge of a very limited number of via-points. FIR filters are the foundation of this result. As a matter of fact the planner is composed by a first FIR filter for the computation of the control points from the sequence of desired via-points, followed by a chain of moving average filters. Therefore, the generator combines the characteristics of B-spline trajectories (smoothness and minimum curvature) and those of FIR filters (simple structure and computational efficiency). Moreover, besides standard cubic curves, the so-called smoothing B-splines have been considered for online trajectory generation. This allows to find a tradeoff between the possibility of exactly crossing the given via-points and the smoothness of the resulting trajectory. A simple teleoperation task with a Puma 560 industrial manipulator has been arranged for experimentally validating the proposed method.

Position/force control of an arm/gripper system for space manipulation

In advanced robotics applications, as those foreseen in space, some degree of dexterity and autonomy is necessary in order execute tasks in unstructured environments. For this purpose besides the kinematic configuration of the device other basic issues are the sensorial equipment and proper control strategies. The paper presents an experimental activity for the validation of a robotic gripper for space applications. In particular the project foresees the compatibility of the gripper with the EUROPA arm, developed by ASI and Tecnospazio. The key points of the gripper design are the wide working space compared with its physical dimensions and the capability to deal with free-flying objects in zero-gravity conditions. This capability is achieved by using proximity and force/torque sensors and by properly controlling and coordinating the gripper and the carrying arm. After a brief illustration of the main features of the gripper, the experimental activity is presented and the results achieved so far are discussed.