Capturing large objects of unknown shape and orientation remains a challenge for most robotic grippers. We present a highly under-actuated gripper well suited for this task. Prior work shows two primary limitations to these grippers: the grip force of each link tends to decrease as the number of links increases, and the stability of an under-actuated linkage depends on the configuration of the links so grippers with many links are unlikely to be stable for arbitrary surfaces. We address these concerns by implementing two complementary methods of stabilization: using high-friction materials and scaling forces into the surface. We show that gecko-inspired adhesives provide an adhesion-controlled friction that can stabilize the gripper and improve grasp performance without the need of large normal forces. The under-actuated linkages also conform around arbitrary shapes and provide capability beyond prior adhesion-based grippers. With these high-friction interfaces, we show highly under-actuated linkages successfully grasp in many configurations without strict stability. The gripper is capable of holding over 30 N and consists of two tendon driven linkages that are each 65 cm long. This type of gripper is well suited for tasks without a predefined target geometry or orientation such as satellite servicing.

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.

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 pad's 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.

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.

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.