Rocco Vertechy

Design of a Single-Acting Constant-Force Actuator Based on Dielectric Elastomers

The interest in actuators based on dielectric elastomer films as a promising technology in robotic and mechatronic applications is increasing. The overall actuator performances are influenced by the design of both the active film and the film supporting frame. This paper presents a single-acting actuator, which is capable of supplying a constant force over a given range of motion. The actuator is obtained by coupling a rectangular film of silicone dielectric elastomer with a monolithic frame designed to suitably modify the force generated by the dielectric elastomer film. The frame is a fully compliant mechanism whose main structural parameters are calculated using a pseudo-rigid-body model and then verified by finite element analysis. Simulations show promising performance of the proposed actuator.

Development of a new exoskeleton for upper limb rehabilitation

This paper deals with the development of a novel exoskeleton for the robotic rehabilitation of upper extremities. The system is based on modular custom-designed actuation groups implementing high reduction ratios and redundant position measurement for securing patient safety, and joint torque sensing for guaranteeing system performance and providing application flexibility. Experimental results of the special component prototypes are reported which confirm the validity of the developed actuation groups and the potentials of the proposed exoskeleton architecture.

A Compound-Structure Frame for Improving the Performance of a Dielectric Elastomer Actuator

Actuators based on Dielectric Elastomer films have been rising as a promising technology in robotic and mechatronic applications. Their overall behavior is highly influenced by the geometry and structural properties of the frame that is coupled with the active film. In this paper, a compound-structure compliant frame is proposed with the aim of obtaining an actuator capable of providing a quasi-constant force over a certain range of motion. A “diamond” shaped frame, designed to support the pre-stretched active film, is coupled with a “delta” shaped element, designed to modify the overall actuator stiffness and improve its performance. Both the diamond and the delta element are fully compliant mechanisms whose main structural parameters are calculated using pseudo-rigid-body models and then verified through finite element analysis. Simulations show promising performance of the proposed actuator.

Design of a linear dielectric elastomer actuator of conical shape with quasi-constant available thrust

A novel design for a Dielectric Elastomer (DE) actuator is presented. The actuator is obtained by coupling a conically shaped DE film with a compliant mechanism. The compliant mechanism is designed to suitably modify the force generated by the elastomer film. The resulting actuator provides a nearly constant force along the entire actuator stroke when the DE film is activated and quickly returns to an initial rest position when the DE film is deactivated. The electromechanical properties of the DE film are measured experimentally. The sizing of the compliant mechanism is obtained through a pseudo-rigid-body model and subsequently verified through finite element analysis. Simulations show that the designed actuator works as desired. Possible applications of this kind of actuator are MRI compatible devices, haptic devices and Braille cells.

Experimental evaluation of optimal conically-shaped Dielectric Elastomer linear actuators

A conically shaped Dielectric Elastomer (DE) linear actuator is presented which is obtained by coupling a DE film with a compliant mechanism. The compliant mechanism is designed, by means of a pseudo-rigid-body model, to suitably modify the force generated by the elastomer film. The resulting actuator provides a nearly constant force along the entire actuator stroke when the DE film is activated and returns to an initial rest position when the DE film is deactivated. Experimental activity fully validates the proposed concept. Possible applications of this kind of actuator are Braille cells, light weight robots and haptic devices.

Kinematic analysis of partially decoupled fully-parallel manipulators of type 5-5 and 4-5

This paper presents two fully parallel manipulators of type 5-5 and 4-5 with special geometry that makes them partially decoupled. The direct kinematic analysis and the singularity study of these manipulators are addressed, which show that the motion of the manipulators can be easily controlled. Computational considerations are reported, which demonstrate that the algorithms proposed for the direct kinematic analysis are very efficient. Moreover, a comparison with other special geometries illustrates that the proposed manipulators are valuable solutions and represent a good compromise between an efficient controllability and a simple practical feasibility.

A Fast and Robust Hybrid Method for the Solution of the 6-3 Stewart-Gough Platform Direct Position Analysis

A robust and accurate hybrid method for the real-time estimation of the actual configuration of 6-3 Stewart-Gough platforms is presented. The method is hybrid since on one hand it requires the use of three extra sensors in addition to the six ones, which measure the lengths of the manipulator legs, and on the other hand it reduces the influence of sensor noise on the pose estimate by means of either an iterative procedure, which is based on the Newton-Raphson scheme, at regular configurations, or by means of a noniterative procedure, which is based on the study of the null-space of the manipulator Jacobian, in the vicinity of singular configurations. The method is robust since it does not fail near singular configurations and it detects the actual assembly mode of the manipulator. It is also accurate since it always provides a solution, which satisfies the kinematic constraint equations of the manipulator and is rather insensitive to sensor noise. The method is fast since the estimation of the actual configuration of the mechanism requires a limited number of operations, which can be executed in real-time. Analytical and numerical results are reported to show the robustness, accuracy, and computational efficiency of the proposed method.

A New Procedure for the Optimization of a Dielectric Elastomer Actuator

A novel mathematical procedure is proposed, which makes it possible to optimize lozenge-shaped dielectric-elastomer-based linear actuators for known materials and desired force/stroke requirements. Simulation results are provided which both demonstrate the efficacy of the novel procedure with respect to traditional design approaches and show that simpler, cheaper, lighter and betterbehaved lozenge-shaped actuators can be conceived which do not require any integration of compliant frame elements.