Abstract
This paper presents a novel truss-shaped variable-stiffness deployable robotic grasper to grasp large unknown objects, the grasper comprises a series of basic modules and has the advantages of a large workspace, adjustable stiffness, and a high deploy/fold ratio. First, detailed mechanism designs of the grasper and variable-stiffness joint are introduced, and a mobility analysis and variable stiffness analysis are conducted. Second, the structural analysis of the basic module is carried out, by which several major indices, including deploy/fold ratio, grasping angle, deployment angle, grasping torque, and deployment torque, can be calculated. Third, kinematic analysis is presented to provide the workspace and kinematic simulation, and then the joint trajectory planning based on fifth-order polynomial is also conducted. Fourth, the condition of stable grasp is analyzed and a mathematical model of grasping motion is established. Adam optimization algorithm is then applied to optimization of the mathematical model and a grasping simulation is performed with objects of various sizes and for various working states of the variable-stiffness joint. Finally, a simple physical prototype is fabricated, and variable-stiffness experiments and grasping experiments confirm that the proposed grasper shows excellent grasping performance.
Highlights
Robotic graspers have become a hot topic and the subject of many studies [1]–[5], which can be mainly divided into soft robotic graspers and rigid robotic graspers
The design ideas of soft robotic graspers usually come from natural biology such as earthworm, starfish, and octopus, which are always fabricated by some soft materials such as rubber and shape memory alloy
The main actuators of soft robotic graspers include pneumatic driving and hydraulic driving, these two types of actuators have the advantages of light weight, low price, and convenient operation
Summary
Robotic graspers have become a hot topic and the subject of many studies [1]–[5], which can be mainly divided into soft robotic graspers and rigid robotic graspers. C. Gao et al.: Design and Analysis of a Novel Truss-Shaped Variable-Stiffness Deployable Robotic Grasper grasping mechanisms increases rapidly as the number of basic modules increases, so the mechanism cannot be conveniently transported and stored, especially when grasping large unknown objects [20]. Based on above analysis of soft robotic graspers and rigid robotic graspers, a novel robotic grasper should be proposed to utilize their advantages and avoid their disadvantages, which requires the grasper can be used to grasp large scale and large mass unknown objects and has grasping flexibility To solve such challenge, deployable grasping mechanisms and variable-stiffness grasping mechanisms are worthy of consideration.
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