Aaron Parness

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.

Dynamic surface grasping with directional adhesion

Dynamic surface grasping is applicable to landing of micro air vehicles (MAVs) and to grappling objects in space. In both applications, the grasper must absorb the kinetic energy of a moving object and provide secure attachment to a surface using, for example, gecko-inspired directional adhesives. Functional principles of dynamic surface grasping are presented, and two prototype grasper designs are discussed. Computer simulation and physical testing confirms the expected relationships concerning (i) the alignment of the grasper at initial contact, (ii) the absorption of energy during collision and rebound, and (iii) the force limits of synthetic directional adhesives.

Anchoring foot mechanisms for sampling and mobility in microgravity

An omni-directional anchoring mechanism is presented that can withstand forces greater than 100 N on natural rock surfaces. The anchor builds upon previous development of microspine toes for climbing robots. This work utilizes an opposed octagonal scissor configuration with rows of 30 toes on each lever arm, splayed around a central housing. This anchor design is being developed for the Lemur IIb mobile robot. The anchor can also be used to support a coring drill. The work enables both mobility and sampling in microgravity environments, like the surface of Near Earth Asteroids.

Gravity‐independent Rock‐climbing Robot and a Sample Acquisition Tool with Microspine Grippers

A rock-climbing robot is presented that can free climb on vertical, overhanging, and inverted rock faces. This type of system has applications to extreme terrain on Mars or for sustained mobility on microgravity bodies. The robot grips the rock using hierarchical arrays of microspines. Microspines are compliant mechanisms made of sharp hooks and flexible elements that allow the hooks to move independently and opportunistically grasp roughness on the surface of a rock. This paper presents many improvements to early microspine grippers, and the application of these new grippers to a four-limbed robotic system, LEMUR IIB. Each gripper has over 250 microspines distributed in 16 carriages. Carriages also move independently with compliance to conform to larger, cm-scale roughness. Single gripper pull testing on a variety of rock types is presented, and on rough rocks, a single gripper can support the entire mass of the robot (10 kg) in any orientation. Several sensor combinations for the grippers were evaluated using a smaller test-gripper. Rock-climbing mobility experiments are also described for three characteristic gravitational orientations. Finally, a sample acquisition tool that uses one of the robots grippers to enable rotary percussive drilling is shown.

Controllable ON-OFF adhesion for Earth orbit grappling applications

ON-OFF adhesives can benefit multiple Earth orbit applications by providing the capability to selectively anchor two surfaces together repeatedly and releasably without significant preload. Key to this new capability, targets will not need special preparation; ON-OFF adhesives can be used with cooperative and non-cooperative objects, like defunct satellites or space debris. Using an ON-OFF adhesive gripper allows large surfaces on a target to serve as potential grapple points, reducing the precision needed in the sensing and control throughout the grapple operation. A space-rated adhesive structure is presented that can be turned ON-OFF using a slight sliding motion. This adhesive mimics the geometry and performance characteristics of the adhesive structures found on the feet of gecko lizards. Results from adhesive testing on common orbital surfaces like solar panels, thermal blankets, composites, and painted surfaces are presented. Early environmental testing results from cold temperature and vacuum tests are also presented. Finally, the paper presents the design, fabrication, and preliminary testing of a gripping mechanism enabled by these ON-OFF adhesives in preparation for satellite-servicing applications. Adhesive levels range from near zero on rough surfaces to more than 75 kPa on smooth surfaces like glass.

Scaling controllable adhesives to grapple floating objects in space

As the number of rocket bodies and other debris in Earths orbit increases, the need to capture and remove this space junk becomes essential to protect new satellites. A low cost solution may include gecko-inspired directional adhesives, which require almost no compressive preload to generate adhesion and are therefore suitable for surface grasping in space where objects are free floating. Current individual adhesive units with a pair of opposed pads achieve a limit of 13N normal to the surface. Instead of using a single large unit to generate high levels of adhesion, using multiple small gripper units is desirable to prevent single-point failures and to conform to higher curvatures. For this strategy to succeed, it is essential to distribute the overall force evenly, to minimize the overall preload normal to the surface, and to prevent local failures from propagating over the array. We present two load sharing mechanisms. The first uses nearly-constant force springs in parallel. The second uses a tendon and pulleys in series. Both allow a 4-unit gripper to maintain the same adhesive stress as a single unit. A normal adhesive load to compressive preload ratio of 100:1 is demonstrated. Zero gravity experiments and air bearing floor experiments demonstrate the grippers functionality in a simulated space environment. Design considerations are discussed for further scaling, with the trade-offs among load sharing, suitability for different surfaces, and failure sensitivity.

A robotic device using gecko-inspired adhesives can grasp and manipulate large objects in microgravity

A load-sharing robotic device can grasp, manipulate, and release objects in microgravity using space-qualified dry adhesives. Grasping and manipulating uncooperative objects in space is an emerging challenge for robotic systems. Many traditional robotic grasping techniques used on Earth are infeasible in space. Vacuum grippers require an atmosphere, sticky attachments fail in the harsh environment of space, and handlike opposed grippers are not suited for large, smooth space debris. We present a robotic gripper that can gently grasp, manipulate, and release both flat and curved uncooperative objects as large as a meter in diameter while in microgravity. This is enabled by (i) space-qualified gecko-inspired dry adhesives that are selectively turned on and off by the application of shear forces, (ii) a load-sharing system that scales small patches of these adhesives to large areas, and (iii) a nonlinear passive wrist that is stiff during manipulation yet compliant when overloaded. We also introduce and experimentally verify a model for determining the force and moment limits of such an adhesive system. Tests in microgravity show that robotic grippers based on dry adhesion are a viable option for eliminating space debris in low Earth orbit and for enhancing missions in space.

Inchworm style gecko adhesive climbing robot

We present a gecko-adhesive enabled robot that can climb surfaces in any gravitational orientation or operate in full zero gravity. The robot is a prototype for inspection applications aboard the International Space Station (ISS) both inside and outside the station. A specific area of interest for this paper is a narrow gap, approximately 1.5 inches wide, behind internal equipment racks. The prototype robot uses oppositional pairs of gecko adhesive pads that turn the van der Waals adhesion ON and OFF using an applied shear load. The robot is currently teleoperated and utilizes an inchworm style gait. The robot can turn in a tight circle, fits within a 1.5 inch gap, and can transition between orthogonal surfaces. The gecko adhesives leave no residue, are highly reusable, and create strong adhesion in vacuum and across a wide temperature range. The robot design and initial experimental results are presented including climbing vertical walls in Earths gravity.

Asteroids: Anchoring and Sample Acquisition Approaches in Support of Science, Exploration, and In situ Resource Utilization

The goal of this chapter is to describe technologies related to asteroid sampling and mining. In particular, the chapter discusses various methods of anchoring to a small body (a prerequisite for sampling and mining missions) as well as sample acquisition technologies and large scale mining options. These technologies are critical to enabling exploration, and utilization of asteroids by NASA and private companies.

Demonstrations of gravity-independent mobility and drilling on natural rock using microspines

The video presents microspine-based anchors being developed for gripping rocks on the surfaces of comets and asteroids, or for use on cliff faces and lava tubes on Mars. Two types of anchor prototypes are shown on supporting forces in all directions away from the rock; >;160 N tangent, >;150 N at 45°, and >;180 N normal to the surface of the rock. A compliant robotic ankle with two active degrees of freedom interfaces these anchors to the Lemur IIB robot for future climbing trials. Finally, a rotary percussive drill is shown coring into rock regardless of gravitational orientation. As a harder-than-zero-g proof of concept, inverted drilling was performed creating 20mm diameter boreholes 83 mm deep in vesicular basalt samples while retaining 12 mm diameter rock cores in 3-6 pieces.