An Underactuated Finger Mechanism With Self-Adaptive Capability

With the development of smart and intelligent machinery, the mechanical structurewhich can automatically adapt to the external environment and different object has becomea hot point among domestic and foreign researchers. Due to the capability of automaticallyadapting its configuration to grasped objects, anthropomorphic hands have been used inrobotics and engineering applications and made great achievements. As a member ofself-adaptive robotic hands, dexterous hands have strong grasp ability, while they own thecharacters of multi fingers, multi DOFs and multi actuators, resulting in a bad reliabilityand limit application. An underactuated hand also is multi-finger, multi-joint andmulti-DOF, and its number of actuators is smaller than its number of degrees of freedom.In addition, owing to its fewer actuators, an underactuated has a simpler driver mechanismand control system, while ensuring the capability of automatically adapting itsconfiguration to grasped objects. As a result, underactuated hands have received extensiveattention among researchers and have been an important field of robotic research.The design of finger mechanism is the basis for designing an underactuated hand, andthe design and application of variable constraints is the key to ensure the reliability andstability of the hand in a grasping process. This paper focuses on the design ofunderactuation mechanism, the dimensional synthesis and the force capability of theunderactuated finger. The details are as follows:(1) Even symmetry slider-double-crank mechanism was obtained through theevolution of odd symmetry slider-double-crank mechanism. Then, an underactuated fingermechanism with variable constraints was proposed based on even symmetryslider-double-crank mechanism.(2) The mathematical model of the finger mechanism was built through kinematic andstatic analysis. Then, an objective function was established according to the designrequirements, and an optimal solution was obtained by using MATLAB optimal function.The numerical results meet the design requirements.(3) At first, the number and the orientation of the fingers as well as the distancebetween them was determined on the basis of the criterion that the robotic hands are capable of giving strong and accurate grasp to objects regularly or irregularly. Next, it wasproposed that the effects of the radius, X-offset and Y-offset of a cylinder to the grasp forceof the finger as well as the hand. Then, the weight of the object that can be grasped wasgiven when the finger is in the critical contact condition. After that, the relationshipbetween driving force and force isotropy in the middle configuration was obtained. Later,the force capability and its distribution of underactuated finger were proposed. At last, thedexterity of finger mechanism was obtained within the workspace.(4) Virtual prototype analysis of the finger mechanism was carried out to validate theability of grasping irregular objects with ADAMS. The analysis obtains the expectedeffect.The results of this paper will enrich and expand the design theory and method ofanthropomorphic robot hands, as well as innovative design method and application ofself-adaptive mechanism, and has important theoretical and practical value.