Adhesion State Estimation for Electrostatic Gripper Based on Online Capacitance Measure

Electroadhesion is a suitable technology for developing grippers for applications where fragile, compliant or variable shape objects need to be grabbed and where a retention action is typically preferred to a compression force. This article presents a self-sensing technique for electroadhesive devices (EAD) based on the capacitance measure. Specifically, we demonstrate that measuring the variation of the capacitance between electrodes of an EAD during the adhesion can provide useful information to automatically detect the successful grip of an object and the possible loss of adhesion during manipulation. To this aim, a dedicated electronic circuit is developed that is able to measure capacitance variations while the high voltage required for the adhesion is activated. A test bench characterization is presented to evaluate the self-sensing of capacitance during different states: (1) the EAD is far away from the object to be grasped; (2) the EAD is in contact with the object, but the voltage is not active (i.e., no adhesion); and (3) the EAD is activated and attached to the object. Correlation between the applied voltage, object material and shape and capacitance is made. The self-sensing EAD is then demonstrated in a closed-loop robotic application that employs a robot manipulator arm to pick and place objects of different kinds

Design and experimental characterization of a high performance hydrostatic transmission for robot actuation

This paper introduces a hydrostatic torque-transmission for robotic applications based on rolling diaphragm cylinders. The proposed design solution, that relies on a novel floating-cylinder architecture, can be effectively employed for the implementation of robots with actuators that are remotely located with respect to their kinematic structure, without sacrificing performance and controllability. A prototype of proposed system is designed and implemented to comply with requirements for the actuation of a robotic arm exoskeleton. Such a system brings together a set of interesting attributes such as an extremely low level of friction (< 0.8 % of rated torque), transparent torque transmission (with average errors in open-loop sinusoidal torque-tracking in the range of 0.2–0.4 Nm), high torque (in the range of 30Nm), large force bandwidth (20–30 Hz), large range of motion (> 140 ∘), simple design, ease in assembling, low-cost, reduced encumbrance (compatible with the integration with robotic links) and lightweight. Additionally, we demonstrate that the presented system allows to integrate a very accurate pressure-based output torque estimation which can be employed to further improve the system performance without the use of strain-based load-cells

Smith-Predictor-Based Torque Control of a Rolling Diaphragm Hydrostatic Transmission

Rolling Diaphragm Hydrostatic Transmissions (RDHT) are high-performance low-cost solutions to delocalize heavy actuators away from the joints of robotic systems. Exploiting a low-cost pressure-based sensing technique, we propose here a Smith-predictor-based joint torque control of an RDHT-based actuation system. We also use a load-cell sensor for ground truth validation. The developed feedback controller is conveniently tuned based on an arbitrary pre-specified closed-loop natural frequency and damping ratio. This preserves the open-loop bandwidth while removing the intrinsic oscillations of the lightly damped highly transparent open-loop plant. Experimental tests validate the proposed control strategy, both in a stand-alone torque setpoint configuration and in a series of Human-Robot-Interaction tests confirming the significant advantages of the closed-loop control architecture

Electrostatic bellow muscle actuators and energy harvesters that stack up

Future robotic systems will be pervasive technologies operating autonomously in unknown spaces that are shared with humans. Such complex interactions make it compulsory for them to be lightweight, soft, and efficient in a way to guarantee safety, robustness, and long-term operation. Such a set of qualities can be achieved using soft multipurpose systems that combine, integrate, and commute between conventional electromechanical and fluidic drives, as well as harvest energy during inactive actuation phases for increased energy efficiency. Here, we present an electrostatic actuator made of thin films and liquid dielectrics combined with rigid polymeric stiffening elements to form a circular electrostatic bellow muscle (EBM) unit capable of out-of-plane contraction. These units are easy to manufacture and can be arranged in arrays and stacks, which can be used as a contractile artificial muscle, as a pump for fluid-driven soft robots, or as an energy harvester. As an artificial muscle, EBMs of 20 to 40 millimeters in diameter can exert forces of up to 6 newtons, lift loads over a hundred times their own weight, and reach contractions of over 40% with strain rates over 1200% per second, with a bandwidth over 10 hertz. As a pump driver, these EBMs produce flow rates of up to 0.63 liters per minute and maximum pressure head of 6 kilopascals, whereas as generator, they reach a conversion efficiency close to 20%. The compact shape, low cost, simple assembling procedure, high reliability, and large contractions make the EBM a promising technology for high-performance robotic systems