This paper introduces a new four-limbed robot, LEMUR 3, that has demonstrated climbing on cliff faces and smooth glass. Each limb on the robot consists of seven identical actuators in a serial chain. Each limb terminates in a single axis force sensor that allows various end effectors to be mounted and connected to the robot's power and communication system. Microspine grippers were used for climbing the rocky surface and gecko adhesive grippers were used for the glass solar panels. All other hardware and much of the software was common for the two demonstrations. The robot's mechanical, electrical, and software systems, various gripping devices, and field demonstrations are described. Limbed mobility is of interest to JPL and NASA because of its potential to access extreme terrain, including that on Mars and in microgravity environments.

We demonstrate a flexible, electrostatic adhesive gripper designed to controllably grasp and manipulate soft goods in space. The 8-fingered gripper has 50 cm2of active electrodes operating at 3 kV. It generates electrostatic adhesion forces up to 3.5 N (0.70 kPa) on Ge-coated polyimide film and 1.2 N on MLI blanket, a film composite used for satellite thermal insulation. Extremely low-force gripper engagement (0.08 N) and release (0.04 N) of films is ideal for micro-gravity. Individual fingers generate shear adhesion forces up to 4.76 N (5.04 kPa) using electrostatic adhesive and 45.0 N (47.6 kPa) with a hybrid electrostatic / gecko adhesive. To simulate a satellite servicing task, the gripper was mounted on a 7-DoF robot arm and performed a supervised grasp, manipulate, and release sequence on a hanging, Al-coated PET film.

As the number of rocket bodies and other debris in Earth's 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 gripper's 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.

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 adhesive's 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 adhesive's 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.

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 Earth's gravity.

ON-OFF adhesives can benefit manufacturing and space applications by providing the capability to selectively anchor two surfaces together repeatedly and releasably without significant preload. Two key areas of concern are speed of engagement and sensing the quality of that engagement. Here we describe a dual-purpose proximity and tactile sensor for the contact surfaces of robotic systems. Using infrared emitters and combinations of wide and narrow angle detectors, this device combines proximity and force sensing to seamlessly transition from a pre-contact to contact state. As an inherently low-power device, it is amenable to mobile robotic applications. We also present results showing this engagement can occur very rapidly, making it useful in high-throughput manufacturing and dexterous manipulation tasks.

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.

JPL has developed the worlds first rock climbing robot. This video presents climbing trials at vertical, overhanging, and inverted angles, and a zero-g drill for astronauts.

This video introduces a small, new reconnaissance robot that can climb concrete surfaces up to 85° at a rate of 25cm*s-1, make rapid horizontal to vertical transitions, carry an audio/visual payload, and survive impacts from 3m. The robot can travel over 45 cm*s-1on flat ground, and turn in place. The Durable Reconnaissance and Observation Platform, D.R.O.P., is manufactured using a combination of selective laser sintering (SLS) and shape deposition manufacturing (SDM) techniques. The enabling feature of DROP is the use of microspines in a rotary configuration, increasing climbing and walking speed over previous microspine-based robots by more than 5x. The robot uses a 180mAh LiPo battery, Baby Orangutan microprocessor, and two brushed DC motors.

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.

To grip rocks on the surfaces of asteroids and comets, and to grip the cliff faces and lava tubes of Mars, a 250 mm diameter omni-directional anchor is presented that utilizes a hierarchical array of claws with suspension flexures, called microspines, to create fast, strong attachment. Prototypes have been demonstrated on vesicular basalt and a'a lava rock supporting forces in all directions away from the rock. Each anchor can support >;160 N tangent, >;150 N at 45°, and >;180 N normal to the surface of the rock. A two-actuator selectively-compliant ankle interfaces these anchors to the Lemur IIB robot for climbing trials. A rotary percussive drill was also integrated into the anchor, demonstrating self-contained rock coring regardless of gravitational orientation. As a harder-than-zero-g proof of concept, 20mm diameter boreholes were drilled 83 mm deep in vesicular basalt samples, retaining a 12 mm diameter rock core in 3-6 pieces while in an inverted configuration, literally drilling into the ceiling.

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 lib 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.

Prior research in biology and mechanics has shown the importance of hierarchy to the performance of dry adhesive systems on rough surfaces. The gecko utilizes several levels of hierarchy that operate on length scales from millimeters to 100s of nanometers in order to maneuver on smooth and rough vertical surfaces ranging from glass to rock. The gecko's hierarchical system serves two main purposes: it permits conformation to the surface for a large effective area of contact, and it distributes the load evenly among contacting elements. We present a new two-tiered directional adhesive system that provides these capabilities for a gecko-inspired climbing robot. The distal features consist of wedge-shaped structures with a base width of 50 mum and a height of approximately 180 mum. The wedges are mounted atop angled cylindrical features, 380 mum in diameter by approximately 1 mm long. Together, the proximal and distal features bend preferentially in the direction of inclination when loaded with a tangential force, achieving a combination of directional adhesion and conformation to rough surfaces. Using this system, a four legged robot that was previously restricted to climbing smooth surfaces is able to climb vertical surfaces such as a wood panels, painted metals, and plastics. On rougher surfaces, the two-tiered system improves adhesion by a factor of five compared to the wedge features alone. The hierarchical system also improved alignment and performance for large patch sizes.

Recent biological research suggests that reliable, agile climbing on smooth vertical surfaces requires controllable adhesion. In nature, geckos control adhesion by properly loading the compliant adhesive structures on their toes. These strongly anisotropic dry adhesive structures produce large frictional and adhesive forces when subjected to certain force/motion trajectories. Smooth detachment is obtained by simply reversing these trajectories. Each toe's hierarchical structure facilitates intimate conformation to the climbing surface resulting in a balanced stress distribution across the entire adhesive area. By controlling the internal forces among feet, the gecko can achieve the loading conditions necessary to generate the desired amount of adhesion. The same principles have been applied to the design and manufacture of feet for a climbing robot. The manufacturing process of these Directional Polymer Stalks is detailed along with test results comparing them to conventional adhesives.