Micro aerial vehicles (MAV) with multiple rotors, or multicopters, have many promising applications ranging from environmental monitoring, agricultural inspection, to package delivery. These applications, however, usually face a critical problem: the flight time of MAVs is limited due to the low aerodynamic efficiency and high energy consumption. One promising solution is to make them rest on desired objects using perching, an important capability in biological flyers (e.g., birds). In this paper, we present the design and experimentation of a novel perching mechanism: a low cost, 3D printed gripper with bistability (i.e., two stable states). The gripper has two unique characteristics. First, using bistability, it can passively switch from open to closed state using the impact between the gripper and the perching object, alleviating the requirement for precise motion control. Second, the gripper has two perching methods for different objects. For objects with a small height, it can form a closed diamond shape to encircle the objects (encircling method). For objects with a large height, the gripper's two fingers can clip on each side of the objects to utilize the friction forces for perching (clipping method). We analyze the proposed gripper design to predict the required force for opening and closing the gripper. We also predict the size of objects that will allow for successful perching for the clipping method. All the theoretical analyses are experimentally verified. Finally, we integrate the gripper onto a palm-size quadcopter to enable a mechatronic system for perching, and demonstrate successful perching with both clipping and encircling methods as well as aerial grasping. Although our bistable gripper is used with a palm-size quadcopter, the design strategy can also be applied to large-size MAVs for both energy efficient perching and aerial grasping.

Perching onto an object (e.g., tree branches) has recently been leveraged for addressing the limited flight time for flying robots. Successful perching needs a mechanical mechanism to damp out the impact and robustly grasp the object. Generally, such a mechanism requires actuation for grasping. In this article, we present a fully passive mechanism without using any actuator: a mechanically intelligent and passive (MIP) gripper that can be used for either aerial perching or grasping. Initially open, the gripper can be closed by the impact force during perching. After closure, if a sufficient mass (e.g., the robot’s mass) is applied, the gripper can switch to a holding state and maintain that state to hold the mass. Once the mass is removed, the gripper can automatically open. We establish static models for the gripper to predict the required forces for successful state transitions. Based on the models, we develop design guidelines for the gripper so that it can be used for different flying robots with different weights. Experiments are conducted to validate the models. Attaching the gripper onto a quadcopter, we demonstrated aerial perching onto rods and aerial grasping rod-like objects. Because the MIP gripper is lightweight (can reach a mass ratio of 0.75% between the gripper and the grasped object for static grasping), we expect it would be well suited for aerial perching or grasping due to the limited payload capability for flying robotsxv.

Many biological organisms (e.g., insects, birds, and mammals) rely on the perception of an informational variable called time-to-contact (TTC) to control their motion for various tasks such as avoiding obstacles, landing, or interception. TTC, defined as the required time to contact an object if the current velocity is maintained, has been recently leveraged for robot motion control in various tasks. However, most existing robotic applications of TTC simply control the TTC to be constant or constantly decreasing, without fully exploring the applicability for TTC. In this paper, we propose two-stage TTC based strategies and apply them to aerial robotic perching. With the proposed strategies, we can generate reference trajectories for TTC to realize the non-zero contact velocity required by perching, which is impossible for constant or constantly decreasing TTC strategy, but of critical importance for robust perching performance. We conduct simulations to verify the superiority of the proposed strategies in terms of shorter time for perching. Further, with properly designed controllers, we perform experiments on a palm-size quadcopter to track the planned reference trajectories and realize aerial robotic perching. The research presented in this paper can be readily applied to the control of flying robot for perching with visual feedback, and can inspire more alternative forms of TTC based planning and control for robotic applications.

Time-to-contact, a biologically inspired concept, is defined as the time for a moving observer to contact an object or surface if the current velocity is maintained. Since it can be directly estimated from image sequences using a vision sensor, time-to-contact is widely applied for various robotic applications such as docking, chasing, landing, and navigation. Nevertheless, existing estimation methods, such as the size based method and optical flow divergence method, require the time-consuming feature extraction and tracking. In this paper, we adopt a featureless method that can directly estimate time-to-contact using only the image intensity information. Moreover, we propose an error based proportional control algorithm based on the estimated time-to-contact. Such a controller is implemented on a mobile robot platform to achieve real-time docking. We have also proposed a new time-to-contact estimation algorithm considering the robot's angular velocities and verified the result using image sequences. The estimation and control method presented in this paper has the potential to be applied to miniature robots to accomplish agile locomotion with limited computation power or limited sensing modalities.

In this paper, a method for optical localization of discharge sources based on a multi-normal photoelectric array is proposed. The core idea is to use the response of the photoelectric sensor to the ionizing light signal emitted by the partial discharge to achieve angular localization. The main analysis and synthesis steps include: firstly, testing the sensitivity of the photoelectric sensor to capture the discharge light signal; secondly, analyzing the principle of light source tracing based on the normal vector of the 3-dimensional sensor and giving the calculation steps of angular localization based on the proportional response; then, giving the cooperative localization method based on multiple normal vectors to improve the accuracy of light source localization. Finally, the validity of these obtained results is verified by a simple experiment test.