Mechanical design, modeling, and identification for a novel antagonistic variable stiffness dexterous finger

Abstract

This study traces the development of dexterous hand research and proposes a novel antagonistic variable stiffness dexterous finger mechanism to improve the safety of dexterous hand in unpredictable environments, such as unstructured or man-made operational errors through comprehensive consideration of cost, accuracy, manufacturing, and application. Based on the concept of mechanical passive compliance, which is widely implemented in robots for interactions, a finger is dedicated to improving mechanical robustness. The finger mechanism not only achieves passive compliance against physical impacts, but also implements the variable stiffness actuator principle in a compact finger without adding supererogatory actuators. It achieves finger stiffness adjustability according to the biologically inspired stiffness variation principle of discarding some mobilities to adjust stiffness. The mechanical design of the finger and its stiffness adjusting methods are elaborated. The stiffness characteristics of the finger joint and the actuation unit are analyzed. Experimental results of the finger joint stiffness identification and finger impact tests under different finger stiffness presets are provided to verify the validity of the model. Fingers have been experimentally proven to be robust against physical impacts. Moreover, the experimental part verifies that fingers have good power, grasping, and manipulation performance.

Variable stiffness methods for robots: a review

“…For example, they are suitable for manipulation of Background of variable stiffness for robotics: (a) different variable stiffness devices. Reproduced from [21]. CC BY 4.0.…”

“…As shown in figure 1(a), to improve the robots' compliance and safety when they interact with complicated and unstructured environments, many methods based on the concept of stiffness modulation, have been developed. For example, the rigid robotic finger can manipulate different objects based on variable stiffness mechanism [21]; the wearable exoskeletons of rigid robotic arm with variable stiffness can be used for increasing safe physical human-robot interaction or improving the dynamical adaptability with environment, as well as enhancing the energy efficiency [22]; artificial spine can increase its stiffness to support the body's weight and provide load-bearing capabilities, while it also can adaptively decrease stiffness to enable adaptive motion and provide flexibility when necessary [23]; variation in leg stiffness can not only allow the robots to alter their stride frequency, but also can be beneficial to running and hopping systems, allowing energy to be stored and reused as the leg shortens and extends [24,25]; stiffness tunable ankle exoskeletons can adjust output force based on the external load and joint angle, which can provide scientifically motivated, quantifiable, and automated exercises, help control the complex's position during ambulation, and to then recover a normal walking gait for patients [26]. As shown in figure 1(b), some animals and soft organ, such as octopus, snake and elephant trunk show highly flexible and deformable structures in low stiffness, which enable them entrance into small apertures for shelter.…”