1,720,985 research outputs found
Compact series visco-elastic joint (SVEJ) for smooth torque control
No full textThe design and control of a new series-viscous-elastic joint are presented. The proposed joint consists of 3D printed parts compressing nonlinear elastic silicone springs. The use of silicone springs is the main novelty of the system; they exhibit internal damping, which enhances system performance allowing a simpler and more stable control. Their stiffness allows the system to bear a torque of about 4.5 Nm at a deformation angle of about 20 degrees. In this article, the system is modeled using the Neo-Hookean material model and then characterized through experiments to build the joint torque estimator. A proportional torque controller is implemented to evaluate bandwidth, transparency, impedance rendering, and stability, obtaining satisfactory results. The bandwidth ranges from 6.9 to 9.9 Hz depending on chirp input torque amplitude, as the system is nonlinear. The proposed solution is compact and cheap; both the design and the torque controller are suitable for future integration in an exoskeleton, or a cooperative robot, or a haptic device. SVEJ works as a torque sensor and introduces compliance between the motor and the environment, enhancing safety for robotic devices interacting with humans
A Miniature Direct-Drive Hydraulic Actuator for Wearable Haptic Devices based on Ferrofluid Magnetohydrodynamic Levitation
No full textHydraulic and pneumatic actuators in haptics offer the advantage of soft and compliant interfaces, with the drawback of cumbersome driving devices and limited modulation capabilities. We propose a miniature hydraulic actuator based on a linear electromagnetic motor with an embedded ferrofluid sealing. The solution has two main advantages: it shows no static friction due to the magnetohydrodynamic levitation effect of the ferrofluid, and the output force can be scaled (by varying the radius of the actuator) without introducing noise and friction of mechanical reduction mechanisms. Moreover, soft and compliant interfaces in the form of actuated pouches can be obtained on wearable devices with embedded actuators. As a concept prototype, we present here a compact and soft haptic thimble integrating the proposed actuator: experimental characterization at the bench, and perception experiments with the final prototype, evaluate the low-noise rendering capability of the method
Introducing wearable haptics for rendering velocity feedback in VR serious games for neuro-rehabilitation of children
Full text linkRehabilitation in virtual reality offers advantages in terms of flexibility and parametrization of exercises, repeatability, and continuous data recording and analysis of the progress of the patient, also promoting high engagement and cognitive challenges. Still, most of the proposed virtual settings provide a high quality, immersive visual and audio feedback, without involving the sense of touch. In this paper, we show the design, implementation, and first evaluation of a gaming scenario for upper limb rehabilitation of children with cerebral palsy. In particular, we took care to introduce haptic feedback as a useful source of sensory information for the proposed task, considering—at the same time—the strict constraints for haptic wearable devices to comply with patient’s comfort, residual motor abilities, and with the embedded tracking features of the latest VR technologies. To show the potential of haptics in a rehabilitation setup, the proposed device and rendering method have been used to improve the velocity control of upper limb movements during the VR exercise, given its importance as a motor recovery metric. Eight healthy participants were enrolled, and results showed that haptic feedback can lead to lower speed tracking errors and higher movement smoothness, making the proposed setup suitable to be used in a rehabilitation context as a way to promote movement fluidity during exercises
A robotic device for the structural dynamics inspection of railway pantographs through nonlinearity tests
No full textThe railway industry is progressively embracing mechatronics solutions to improve maintenance operations. In this context, we present a robotic device that introduces structural dynamics analysis in railway pantograph inspection. Specifically, an innovative macro-micro actuation extends the bandwidth performance of actual devices, while a force control strategy proved to support the execution of nonlinearity tests via the estimation of the Frequency Response Function for different levels of the input force. Thereupon we show that the exploitation of nonlinearity can enhance the detection of even a minor localized fault
Evaluation of an Exoskeleton-based Bimanual Teleoperation Architecture with Independently Passivated Slave Devices
No full textSearch and rescue robotics is becoming a relevant topic in the last years and the growing number of robotic platforms and dedicated projects is the evidence of the interest in this area. In this context, the possibility to drive a remote robot with an exoskeleton is a promising strategy to enhance dexterity, reduce operator effort and save time. However, the use of haptic feedback (bilateral teleoperation) may lead to instability in the presence of communication delay and more complex is the case of bimanual teleoperation where the two arms can exchange energy. In this work, we present a bimanual teleoperation system based on an exoskeletal master, where multi-degrees of freedom (multi-DoFs) and kinematically different devices are involved. In the implemented architecture the two slaves are managed in parallel and independently passivated using the Time Domain Passivity Approach (TDPA) extended for multi-DoFs devices. To investigate the stability of the architecture we designed two tasks highly related to real disaster scenarios: the first one was useful to verify the system behavior in case of small movements and constrained configurations, whereas the second experiment was designed to involve larger contact forces and movements. Moreover, we compared the effect of both delay and low control loop frequency on the stability of the system when TDPA was applied. From the results, it was evident that the overall system exhibited a stable behavior with the use of the TDPA, even passivating the two slaves independently, under simulated time delay and in presence of a low control loop frequency
Design and Characterization of Modular Soft Components for an Exoskeleton Glove with Improved Wearability
No full textPhysiological and kinematic effects of a soft exosuit on arm movements
No full textBackground: Soft wearable robots (exosuits), being lightweight, ergonomic and low power-demanding, are attractive for a variety of applications, ranging from strength augmentation in industrial scenarios, to medical assistance for people with motor impairments. Understanding how these devices affect the physiology and mechanics of human movements is fundamental for quantifying their benefits and drawbacks, assessing their suitability for different applications and guiding a continuous design refinement. Methods: We present a novel wearable exosuit for assistance/augmentation of the elbow and introduce a controller that compensates for gravitational forces acting on the limb while allowing the suit to cooperatively move with its wearer. Eight healthy subjects wore the exosuit and performed elbow movements in two conditions: with assistance from the device (powered) and without assistance (unpowered). The test included a dynamic task, to evaluate the impact of the assistance on the kinematics and dynamics of human movement, and an isometric task, to assess its influence on the onset of muscular fatigue. Results: Powered movements showed a low but significant degradation in accuracy and smoothness when compared to the unpowered ones. The degradation in kinematics was accompanied by an average reduction of 59.20±5.58% (mean ± standard error) of the biological torque and 64.8±7.66% drop in muscular effort when the exosuit assisted its wearer. Furthermore, an analysis of the electromyographic signals of the biceps brachii during the isometric task revealed that the exosuit delays the onset of muscular fatigue. Conclusions: The study examined the effects of an exosuit on the characteristics of human movements. The suit supports most of the power needed to move and reduces the effort that the subject needs to exert to counteract gravity in a static posture, delaying the onset of muscular fatigue. We interpret the decline in kinematic performance as a technical limitation of the current device. This work suggests that a powered exosuit can be a good candidate for industrial and clinical applications, where task efficiency and hardware transparency are paramount
Characterisation of pressure distribution at the interface of a soft exosuit: Towards a more comfortable wear
No full textThe rapid growth of wearable robots in the last decade requires tackling practical issues that arise from their daily use, among which comfort is of great importance. In this work we quantify the level of comfort of a soft exosuit for the elbow by measuring the distribution of pressures at its interface with the human body. We do so with five different cushioning materials, commonly used in sport equipment and orthoses, and identify the ones exhibiting lower peaks of pressure. Polyethylene sponge and neoprene result in the best padding
Rendering Fine Tactile Feedback With a Novel Hydraulic Actuation Method for Wearable Haptic Devices
Full text linkTiny contact transients prove very informative for dexterous, fine manipulation, both in virtual environments and teleoperation. Yet, it is challenging to obtain such quality of the rendering in compact and highly wearable haptic devices. To this aim we propose a novel miniature hydraulic actuator, aiming at low-noise rendering of tiny tactile signals, fully enclosed in a fingertip haptic device. Its novelty is in the use of ferrofluidic sealings, embedded within a miniature linear electromagnetic motor. The solution has two main advantages: it shows no static friction, due to the magnetohydrodynamic levitation effect of the ferrofluid, and a noiseless hydraulic reduction. Besides, the hydraulic actuator enables the use of a soft and compliant interface for transmission of signals to the fingerpad tissues. We evaluate here a prototype of the actuator implemented in a compact and soft haptic thimble: the low-noise rendering capabilities are evaluated in experiments at the bench and through perception study. Then, in a simplified teleoperation setup, we match one-to-one the pressure rendered by the device with a sensitive pneumatic pressure sensor mounted on a robotic fingertip. Results show that haptic feedback alone (no vision) is able to improve results over the visual condition in terms of maximum exerted pressure
A Lightweight Robotic Device Based on a Micro-Macro Actuation Concept for the Inspection of Railway Pantograph
No full textFunctional verification of railway pantographs is performed within periodic maintenance programs by means of specifically designed automation and robotic devices that can check their structural integrity and correct functionality. In this paper, we present the design and validation of a new portable inspection robotic device that through structural dynamic excitation and passive movement can assess the health status of railway pantographs. The device is endowed with a new actuation system that combines the large range of force attained through a macro-Actuator with the high-frequency capabilities of a micro-Actuator while preserving lightweight structure. The reported design and experiments confirm that excitation transmission by accurate force control can be achieved in the entire frequency range, despite the interaction between actuator and structure, and that simulated defects can be revealed by low and high-frequency alterations
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