| Soft manipulator is a compliant,flexible manipulator that can achieve omnidirectional motion.The soft manipulator has the characteristics of simple structure,high safety,strong environmental adaptability,and strong operability of traditional manipulators.It has high application prospects in industries and fields such as medical rehabilitation,housekeeping services,aquaculture,pipeline maintenance and search.However,the whole or main functional parts of the soft manipulator are made of flexible materials,so there is a problem of low rigidity.Therefore,it is necessary to design a soft manipulator that can improve the rigidity and move flexibly.In this paper,a modular soft manipulator with variable stiffness was designed,and the stiffness and other characteristics of the manipulator were studied.The kinematics models and path planning experiments based on inverse kinematics were completed.The main contents of the paper are as follows:A modular pneumatic soft manipulator which can achieve flexible and stable movement was designed.Every module was composed of the driving part and the rigidity adjustment part.A driving part is composed of 3 fan-shaped driving air chambers symmetrically distributed on the periphery.By controlling the inflating and discharging of the driving air chamber,the manipulator can realize bending,stretching,deflection and other motions.The stiffness adjustment part,which achieved by controlling the negative pressure in the central cavity and squeezing the fibers with air pressure,was composed of a central cavity filled with fibers.A pneumatic control platform was built,and the prototype of the manipulator was tested.The experimental results show that the prototype can achieve omnidirectional bending and stiffness adjustment.In order to solve the insufficient rigidity of the existing soft manipulator,a nylon fiber jamming variable stiffness technology was introduced,which used the slender and flexible characteristics of nylon fiber to solve these problems.The structure,working principle,flexibility and stiffness characteristics of fiber interference were introduced,and the effectiveness of the soft manipulator's variable stiffness was verified through experiments.The influence of structural parameters on the stiffness of the soft manipulator was analyzed from five factors of fiber diameter,internal air pressure,wrap cavity shape,fiber configuration,and fiber filling degree.And up to 4.5 times the increase in stiffness was achieved.At the same time,the influence of fiber jamming on other characteristics of the manipulator was studied through experiments.It was found that the fiber jamming would weaken the bending performance and increase the adaptive stiffness of the soft manipulator.The results showed fiber jamming can enhance the horizontal end output force and impact resistance of the soft manipulator,but it had no effect on the axial end output force.In order to accurately control the motion of the soft manipulator,the forward and inverse kinematics models of the soft manipulator with and without gravity were established based on the piecewise constant curvature method.The accuracy of the kinematics model was verified by experiments.Based on the inverse kinematics considering the effect of gravity,the twomodule soft manipulator was planned for the path of the linear and circular trajectory,and the fixed position grasping and placement test was carried out.Based on the inverse kinematics without considering the effect of gravity,the path planning of the three-module soft manipulator was carried out,and the obstacle avoidance experiment was carried out. |
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