Donald Ruffatto

Improving controllable adhesion on both rough and smooth surfaces with a hybrid electrostatic/gecko-like adhesive

This paper describes a novel, controllable adhesive that combines the benefits of electrostatic adhesives with gecko-like directional dry adhesives. When working in combination, the two technologies create a positive feedback cycle whose adhesion, depending on the surface type, is often greater than the sum of its parts. The directional dry adhesive brings the electrostatic adhesive closer to the surface, increasing its effect. Similarly, the electrostatic adhesion helps engage more of the directional dry adhesive fibrillar structures, particularly on rough surfaces. This paper presents the new hybrid adhesives manufacturing process and compares its performance to three other adhesive technologies manufactured using a similar process: reinforced PDMS, electrostatic and directional dry adhesion. Tests were performed on a set of ceramic tiles with varying roughness to quantify its effect on shear adhesive force. The relative effectiveness of the hybrid adhesive increases as the surface roughness is increased. Experimental data are also presented for different substrate materials to demonstrate the enhanced performance achieved with the hybrid adhesive. Results show that the hybrid adhesive provides up to 5.1× greater adhesion than the electrostatic adhesive or directional dry adhesive technologies alone.

Autonomous perching and take-off on vertical walls for a quadrotor micro air vehicle

This paper details an autonomous perching and take-off method for a quadrotor micro air vehicle (MAV) using a novel dry adhesive gripper on smooth vertical walls. The gripper mechanism uses three directional dry adhesive pads in a triangular configuration. Each pad is equipped with a force sensor that can detect the pads loading condition. A servo motor is used to actuate the attachment and detachment of the gripper, which is mounted in the front of a quadrotor MAV. This makes perching possible by simply flying toward and hitting the target surface. Autonomous control is made possible using a Microsoft Kinect to localize the MAV and a PID controller to control the perching maneuver. Experiments show that a minimum speed of 0.4m/s is required to guarantee a successful perch. Also, in 93% of the experiments in which the MAV hits the target at a speed higher than 0.4m/s, the perching maneuver is successful. To initiate a take-off procedure, a release signal is sent to the servo and the gripper is detached from the wall by pulling the adhesive away from the surface. Once the gripper is detached, the MAV becomes airborne again and the control system stabilizes the flight.

Optimization and experimental validation of electrostatic adhesive geometry

This paper introduces a method to optimize the electrode geometry of electrostatic adhesives for robotic gripping, attachment, and manipulation applications. Electrostatic adhesion is achieved by applying a high voltage potential, on the order of kV, to a set of electrodes, which generates an electric field. The electric field polarizes the substrate material and creates an adhesion force. Previous attempts at creating electro-static adhesives have shown them to be effective, but researchers have made no effort to optimize the electrode configuration and geometry. We have shown that by optimizing the geometry of the electrode configuration, the electric field strength, and therefore the adhesion force, is enhanced. To accomplish this, Comsol Multiphysics was utilized to evaluate the average electric field generated by a given electrode geometry. Several electrode patterns were evaluated, including parallel conductors, concentric circles, Hilbert curves (a fractal geometry) and spirals. The arrangement of the electrodes in concentric circles with varying electrode widths proved to be the most effective. The most effective sizing was to use the smallest gap spacing allowable coupled with a variable electrode width. These results were experimentally validated on several different surfaces including drywall, wood, tile, glass, and steel. A new manufacturing process allowing for the fabrication of thin, conformal electro-static adhesive pads was utilized. By combining the optimized electrode geometry with the new fabrication process we are able to demonstrate a marked improvement of up to 500% in shear pressure when compared to previously published values.

Optimization of Electrostatic Adhesives for Robotic Climbing and Manipulation

This paper investigates the optimization of electrode geometry in electrostatic adhesives to enhance adhesion forces for use in robotic climbing and gripping applications. Electrostatic adhesion provides an attachment mechanism that is both controllable and effective over a wide range of surfaces including conductive, semi-conductive, and insulating materials. The adhesives function by utilizing a set of high voltage electrodes that generate an electric field. This electric field polarizes the substrate material, thus generating an adhesion force. Optimizing the geometry of these conductive electrodes provides enhanced adhesion forces that increase attachment robustness. To accomplish this, FEA software was used to evaluate the generated electric field for a given electrode configuration. A range of electrode widths and gap sizes were evaluated to find the optimal configuration. These findings were compared with experimental results for different pad geometries over a range of surface types. Experimental results indicate that on smooth surfaces the simulation results are representative of the actual recorded adhesion forces. Rough surfaces provide similar trends but with varying optimal configurations, likely due to the level of electric field dispersion.Copyright

Experimental results of a controllable electrostatic/gecko-like adhesive on space materials

Many space applications, such as docking, satellite capture, or robotic inspection, could benefit from the use of a controllable (i.e. on-off) adhesive capable of functioning on a wide range of surfaces. This paper focuses on the experimental results of such an adhesive, which combines the benefits of both electrostatic and directional dry adhesives (i.e. gecko-like adhesives). The electrostatic element consists of a conductive electrode pattern embedded inside a soft silicone polymer dielectric. Between the electrodes and the substrate lies a dry adhesive element comprised of directional fibrillar structures. The combination of these two technologies creates a positive feedback cycle in which, depending on surface roughness and material, adhesive levels can be greater than the sum of the two individual technologies. The electrostatic adhesive serves to initially engage the micro-wedges with the surface substrate. As they engage, the micro-wedges bring the electrostatic element closer to the surface, which further increases its adhesion. This consequently allows more of the dry adhesive micro-wedges to engage, particularly on rough surfaces. This paper presents the results of experimental testing of these adhesives over a range of different space-grade materials. These include different paints, composites, and blankets. Results show that the hybrid adhesive performs up to 7.1× greater than electrostatic adhesives alone.

Experimental evaluation of adhesive technologies for robotic grippers on micro-rough surfaces

This paper presents the performance of a newly developed adhesive that combines an electrostatic adhesive with a directional dry (gecko-like) adhesive. The focus is on the adhesives performance on micro-rough surfaces, which has a large number of applications in robotic mobility and manipulation such as climbing, perching, and grasping. Performance was characterized using shear/normal adhesion pressure limit curves and comparing the new hybrid adhesive to each individual adhesive mechanism and a control. Results show that the electrostatic directional dry adhesive generally performs better than a directional dry adhesive, but that on several surfaces, an electrostatic adhesive with no fibrillar mechanism performs the best. Additionally, the paper introduces a new mechanism that maintains an adhesives compliance on micro-rough surfaces while transmitting shear and normal forces to a rigid structure. The mechanism is experimentally compared to a rigid backing and a gecko-like hierarchical suspension layer. Results show that the mechanism performs the best when subjected to mainly normal loads, but a hierarchical suspension handles shear loads better.

A multi-digit tactile motion stimulator.

BACKGROUND One of the hallmarks of haptic exploration is that it typically involves movement between skin and object. Explored objects may contact multiple digits simultaneously so information about motion must be integrated across digits, a process about which little is known. NEW METHOD To fill this gap, we have developed a stimulator that allows for the simultaneous and independent delivery of motion stimuli to multiple digits. The stimulator consists of individual units that deliver motion with three degrees of freedom: rotation (to produce motion), vertical excursion (to control depth of indentation into the skin) and arm orientation (to control the direction of motion). Each degree of freedom is controlled by a single motor. The compact design of the simulator allows for the side-by-side arrangement of the stimulator units such that they impinge upon adjacent fingers. RESULTS To demonstrate the functionality of the stimulator, we performed a series of psychophysical experiments that investigate the perception of motion on multiple fingers. We find that, while the sensitivity to changes in motion direction is equivalent whether stimuli are presented to the same or to different fingers, the perceived direction of motion depends on the relative configuration of the digits. COMPARISON WITH EXISTING METHODS We replicated the results of previous experiments investigating motion discrimination with a single digit and were able to extend these findings by investigating motion perception across multiple digits. CONCLUSION The novel motion stimulator will be an invaluable tool to investigate how motion information is integrated across multiple digits.

Parameter optimization of directional dry adhesives for robotic climbing and gripping applications

This paper experimentally investigates the optimization of directional dry adhesives that can be used for robotic climbing and gripping applications. Directional dry adhesives are modeled on gecko setae. The adhesives are comprised of arrays of micro-scale polymer stalks. The geometry of the polymer stalks has a significant effect upon their adhesion properties. A set of parameters including stalk thickness, stalk angle, face angle and stalk curvature have been identified as factors that influence both normal and shear adhesion levels. A new micro-resolution rapid prototyping process is used to create adhesives with varying geometry and advanced features such as curved stalks. A series of experimental tests characterize the significance of each parameter. Tests indicate that the new curved stalk geometry presented here can provide the greatest overall adhesion and robustness to variations in pull-off angle.