RESUMO
Gripping, holding, and moving objects are among the main functional purposes of robots. Ever since automation first took hold in society, optimizing these functions has been of high priority, and a multitude of approaches has been taken to enable cheaper, more reliable, and more versatile gripping. Attempts are ongoing to reduce grippers' weight, energy consumption, and production and maintenance costs while simultaneously improving their reliability, the range of eligible objects, working loads, and environmental independence. While the upper bounds of precision and flexibility have been pushed to an impressive level, the corresponding solutions are often dependent on support systems (e.g., sophisticated sensors and complex actuation machinery), advanced control paradigms (e.g., artificial intelligence and machine learning), and typically require more maintenance owed to their complexity, also increasing their cost. These factors make them unsuited for more modest applications, where moderate to semi-high performance is desired, but simplicity is required. In this paper, we attempt to highlight the potential of the tarsal chain principle on the example of a prototype biomimetic gripping device called the TriTrap gripper, inspired by the eponymous tarsal chain of insects. Insects possess a rigid exoskeleton that receives mobility due to several joints and internally attaching muscles. The tarsus (foot) itself does not contain any major intrinsic muscles but is moved by an extrinsically pulled tendon. Just like its biological counterpart, the TriTrap gripping device utilizes strongly underactuated digits that perform their function using morphological encoding and passive conformation, resulting in a gripper that is versatile, robust, and low cost. Its gripping performance was tested on a variety of everyday objects, each of which represented different size, weight, and shape categories. The TriTrap gripper was able to securely hold most of the tested objects in place while they were lifted, rotated, and transported without further optimization. These results show that the insect tarsus selected approach is viable and warrants further development, particularly in the direction of interface optimization. As such, the main goal of the TriTrap gripper, which was to showcase the tarsal chain principle as a viable approach to gripping in general, was achieved.
RESUMO
Insect attachment devices and capabilities have been subject to research efforts for decades, and even though during that time considerable progress has been made, numerous questions remain. Different types of attachment devices are known, alongside most of their working principles, however, some details have yet to be understood. For instance, it is not clear why insects for the most part developed pairs of claws, instead of either three or a single one. In this paper, we investigated the gripping forces generated by the stick insect Sungaya inexpectata, in dependence on the number of available claws. The gripping force experiments were carried out on multiple, standardized substrates of known roughness, and conducted in directions both perpendicular and parallel to the substrate. This was repeated two times: first with a single claw being amputated from each of the animals' legs, then with both claws removed, prior to the measurement. The adhesive pads (arolia) and frictional pads (euplantulae) remained intact. It was discovered that the removal of claws had a detractive effect on the gripping forces in both directions, and on all substrates. Notably, this also included the control of smooth surfaces on which the claws were unable to find any asperities to grip on. The results show that there is a direct connection between the adhesive performance of the distal adhesive pad (arolium) and the presence of intact claws. These observations show collective effects between different attachment devices that work in concert during locomotion, and grant insight into why most insects possess two claws.