Search

Electrotactile stimulation is a highly promising technique for providing sensory feedback information for prosthetics. To this aim, disposable electrodes which are predominantly used result in a high environmental and financial cost when used over a long period of time. In addition, disposable electrodes are limited in their size and configurations. This paper presents an alternative approach based on a 3D printed reusable flexible concentric electrode coated with a conductive graphene ink. Here, we have characterized the electrode and demonstrated its effective performance in electrotactile stimulation and sensory feedback for robotic prosthetic hands.

An effective method of communicating sensory feedback for prosthetics is presented using a combination of mechanical pressure and skin stretch, resulting in a mixture of normal and shear force being applied to the human arm. Stimulations were induced on the subject's forearm by three mechanical cranks, each attached to their own servo motor. Three different crank orientations were tested, each producing a different skin stretch direction, with the results showing that shear force/tangential skin stretch applied longitudinally to the forearm was perceived more easily as it produced the best recognition rate. With minimal training, eighteen able-bodied test subjects were able to recognise six different grips with an accuracy of up to 88%, and achieved an accuracy of 80% when recognising the six grips at two different pressure levels. This sensory feedback mechanism shows potential for a simple, easy to learn stimulation device that could help improve users control and embodiment of their prosthetic device that requires three separate feedback channels.

One of the challenging research questions in soft robotics is the establishment of valid mathematical models and control techniques under limited feedback conditions. A soft robotic system will typically have a continuum or monolithic body seamlessly embodying its actuation and sensing elements, accompanied by mechanical structure, and even the energy source, much like a biological system. In this study, we propose a relay sliding mode controller based on the input - output model (RSMC-IO), which is a simple but effective control approach that does not require a complete system model, to control the tip position of a soft prosthetic finger, which typifies a monolithic soft robotic positioning system. The feedback signal corresponding to the bending angle of each joint of the finger is provided by highly stretchable soft strain sensors made of a silicone (EcoFlex 0010) substrate containing channels filled with carbon paste as the conductive component. An analytical expression between the fingertip and joint angles of the finger is derived and experimentally verified. This expression is accurate enough to estimate the joint positions (i.e. joint angles) as well as the fingertip. The experimental results show the efficacy of the proposed controller, which has not been proposed for prosthetic fingers and similar soft robotic positioning systems before.

This study aims to investigate the effects of various design parameters on the actuation performance of a pneumatic network actuator (PNA), optimise its structure using the finite element method (FEM), and subsequently quantify the performance of the resulting actuator topology experimentally. The effects of the structural parameters, including the operation pressure, the wall thickness and the gap between the chambers, bottom layer thickness, and the geometry of the channel cross section, on the deformation and bending angle of the actuator were evaluated to optimise the performance of the pneumatic actuator. A Global Analysis of Variance (ANOVA) was performed to investigate how the variables affect the mechanical output of the actuator and, thus, the significance of variables affecting the deformation (and bending angle) of the pneumatic actuator was identified. After the parameter optimisation, a pneumatic channel with a 4.5 mm bottom layer thickness, 1.5 mm wall thickness, and 1.5 mm gap between sequential chambers is recommended to perform optimised bending motion for the pneumatic network actuator. The optimised FE model results were verified experimentally. This design optimisation method based on the FEM and ANOVA analysis can be extended to the topology optimisation of other soft actuators.

Any implant or prosthesis replacing a function or functions of an organ or group of organs should be biologically and sensorily integrated with the human body in order to increase their acceptance with their user. If this replacement is for a human hand, which is an important interface between humans and their environment, the acceptance issue and developing sensory-motor embodiment will be more challenging. Despite progress in prosthesis technologies, 50-60 & #x0025; of hand amputees wear a prosthetic device. One primary reason for the rejection of the prosthetic hands is that there is no or negligibly small feedback or tactile sensation from the hand to the user, making the hands less functional. In fact, the loss of a hand means interrupting the closed-loop sensory feedback between the brain (motor control) and the hand (sensory feedback through the nerves). The lack of feedback requires significant cognitive efforts from the user in order to do basic gestures and daily activities. To this aim, recently, there has been significant development in the provision of sensory feedback from transradial prosthetic hands, to enable the user take part in the control loop and improve user embodiment. Sensory feedback to the hand users can be provided via invasive and noninvasive methods. The latter includes the use of temperature, vibration, mechanical pressure and skin stretching, electrotactile stimulation, phantom limb stimulation, audio feedback, and augmented reality. This paper provides a comprehensive review of the non-invasive methods, performs their critical evaluation, and presents challenges and opportunities associated with the non-invasive sensory feedback methods.

In this article, we have established an analytical model to estimate the quasi-static bending displacement (i.e., angle) of the pneumatic actuators made of two different elastomeric silicones (Elastosil M4601 with a bulk modulus of elasticity of 262 kPa and Translucent Soft silicone with a bulk modulus of elasticity of 48 kPa - both experimentally determined) and of discrete chambers, partially separated from each other with a gap in between the chambers to increase the magnitude of their bending angle. The numerical bending angle results from the proposed gray-box model, and the corresponding experimental results match well that the model is accurate enough to predict the bending behavior of this class of pneumatic soft actuators. Further, by using the experimental bending angle results and blocking force results, the effective modulus of elasticity of the actuators is estimated from a blocking force model. The numerical and experimental results presented show that the bending angle and blocking force models are valid for this class of pneumatic actuators. Another contribution of this study is to incorporate a bistable flexible thin metal typified by a tape measure into the topology of the actuators to prevent the deflection of the actuators under their own weight when operating in the vertical plane.

Robotic systems consisting of rigid elements connected to each other with single degree of freedom joints have been studied extensively. Robotic systems made of soft and smart materials are expected to provide a high dexterity and adaptability to their physical environment, like their biological counterparts. Electroactive polymer (EAP) actuators, also known as artificial muscles, which can operate both in wet and in dry environments with their promising features such as a low foot-print in activation and energy consumption, suitability to miniaturization, noiseless, and fully compliant operation can be employed to articulate a soft robotic system. This paper reports on kinematic modeling of a polypyrrolebased EAP actuator which is designed and fabricated to form helical configurations in 3-D from its initially spiral 2-D configuration. Denavit-Hartenberg transformations are combined with the backbone model of the actuator to establish the kinematic model. A parametric model has then been incorporated into the kinematic model to accurately estimate the helical configurations of the EAP actuator as a function of time under an electrical input. Experimental and simulation results, which are in good correlation, suggest that the proposed modeling approach is effective enough to estimate the 3-D helical configurations of the EAP actuator.