Grasping objects that are too large to envelop is traditionally achieved using friction that is activated by squeezing. We present a family of shear-activated grippers that can grasp such objects without the need to squeeze. When a shear force is applied to the gecko-inspired material in our grippers, adhesion is turned on; this adhesion in turn results in adhesion-controlled friction, a friction force that depends on adhesion rather than a squeezing normal force. Removal of the shear force eliminates adhesion, allowing easy release of an object. A compliant shear-activated gripper without active sensing and control can use the same light touch to lift objects that are soft, brittle, fragile, light, or very heavy. We present three grippers, the first two designed for curved objects, and the third for nearly any shape. Simple models describe the grasping process, and empirical results verify the models. The grippers are demonstrated on objects with a variety of shapes, materials, sizes, and weights.

Free-flying robots have the potential to autonomously fulfill a wide range of tasks involving manipulation of objects in space. In this paper we study the design of a wrist mechanism for free-flying robots that are equipped with an adhesive gripper for attaching to objects and surfaces. The wrist and gripper allow the robots to apply moments in addition to forces, which increases their versatility for object manipulation. We apply grasp optimization to establish limitations on the forces/moments that the wrist can impart, subject to adhesion capabilities. Building on these results, we present considerations for tuning a passive wrist mechanism, or controlling an active wrist, to broaden the range of forces and moments that the robot can exert. Our theoretical insights and wrist designs are validated in simulations and on a planar micro-gravity test bed.

Perching can extend the useful mission life of a micro air vehicle. Once perched, climbing allows it to reposition precisely, with low power draw and without regard for weather conditions. We present the Stanford Climbing and Aerial Maneuvering Platform, which is to our knowledge the first robot capable of flying, perching with passive technology on outdoor surfaces, climbing, and taking off again. We present the mechanical design and the new perching, climbing, and takeoff strategies that allow us to perform these tasks on surfaces such as concrete and stucco, without the aid of a motion capture system or off-board computation. We further discuss two new capabilities uniquely available to a hybrid aerial-scansorial robot: the ability to recover gracefully from climbing failures and the ability to increase usable foothold density through the application of aerodynamic forces. We also measure real power consumption for climbing, flying, and monitoring and discuss how future platforms could be improved for longer mission life.

We present a new palm design that features a dense array of micro-spines for the JPL Robosimian human-scale climbing robot. A linearly-constrained spine mechanism is introduced and analyzed using adhesion and stiffness models. This mechanism achieves a spine density of 19/cm2and a mean adhesion of 67N (207kPa) on coarse concrete surfaces. The models are validated on two different surfaces with two sets of experiments. A 120×100mm palm consisting of 12 spine tiles and a pulley differential system for load sharing are designed and tested on 9 different surfaces. The mean shear adhesion goes up to 710N (183kPa) on concrete blocks. Design considerations include scaling efficiency and maximal single-spine force. Desirable properties for load sharing in the palm design are discussed.

Nearly all robotic grippers have one trait in common: they grasp objects with normal forces, either directly, or indirectly through friction. This method of grasping is effective for objects small enough for a given gripper to partially encompass. However, to grasp larger objects, significant grip forces and a high coefficient of friction are required. We present a new grasping method for convex objects, using almost exclusively shear forces. We achieve shear grasping with a gripper that utilizes thin film gecko-inspired fibrillar adhesives that conform to the curvature of the object. We present a verified model for grasping a range of curvatures and results that demonstrate the thin film fibrillar adhesives' increased contact area on textured surfaces when loaded in shear. Finally, the gripper is implemented on a robotic arm and grasps a variety of convex objects (at rest and ballistic).

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.

Perching on a vertical surface carries the risk of severe damage to the vehicle if the maneuver fails, especially if failure goes undetected. We present a detection method using an onboard 3-axis accelerometer to discriminate between perching success and failure. An analytical model was developed to calculate acceleration differences for success and failure and set decision times. Two distinct decision times were shown to be effective, corresponding to properly engaging the gripper and overloading the gripper's capabilities. According to a machine learning feature selection algorithm, the maximum Z axis acceleration of the quadrotor and the presence of near-zero readings are the most relevant features within these two time frames. Using these features, the detection algorithm discriminated between success and failure with a 91% accuracy at 40 ms, and 94% at 80 ms. Real-time detection and failure recovery experiments with a 20 g quadrotor verify the detection method. An improved approach that combines various decision times correctly identified success/failure for all 20 trials with an average total falling distance of 0.8m during recovery. We discuss the feasibility of extending our method to other quadrotor platforms.

Adhesion quality sensing is critical to the performance of any robot that utilizes gecko-inspired dry adhesives for climbing, perching, or grasping. We present a 3-axis tactile sensor designed for this application that demonstrates performance on par with a large commercial load cell while being compact enough to integrate into a robot foot. The sensor can measure spatially distributed force loads and demonstrates high sensitivity in both shear and normal components. Results showcase the sensor's ability to detect a variety of unreliable contact and loading conditions before the onset of adhesion failure.

Perching allows Micro Aerial Vehicles (MAVs) avoid the power costs and electrical and acoustic noise of sustained flight, for long-term surveillance and reconnaissance applications. This paper presents a dynamic model that clarifies the requirements for repeatable perching on walls and ceilings using an opposed-grip mechanism and dry adhesive technology. The model predicts success for perching over a range of initial conditions. The model also predicts the conditions under which other directional attachment technologies, such as microspines, will succeed. Experiments conducted using a launching mechanism for a range of different landing conditions confirm the predictions of the model and provide insight into future design improvements that are possible by modifying a few key damping and stiffness parameters.

Telerobotics has the potential to facilitate the repair of satellites in geosynchronous orbit by allowing human operators to interact naturally with remote objects. Time delays on the order of seconds make it difficult to provide immersive feedback to the operator, motivating the use of predictive visual and haptic displays of the robot and environment. A teleoperation framework developed for this scenario invokes a two-part environment model that predicts motion of objects in the environment, both in free space and during contact with the robot. When objects in the environment are in free space, a propagated model using delayed data provides predictive feedback to the operator. However, when the robot interacts with the environment, a local environment model that does not propagate delayed data is used. This reduces computational load and ensures stability during robot-environment interactions. Two experiments were carried out to test the teleoperation system. Results demonstrate the ability of the prediction algorithm to provide reliable feedback and improve operator performance before, during, and after robot-environment interactions.

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.