Design And Control Of Self-adaptive Compliant Underactuated Gripper

Grasping is a typical form of robotic end-operation,which is widely used in sorting and assembly,agricultural picking,disaster rescue,micro-manipulation and other fields.For a variety of operated objects under uncertainty,realizing a stable and safe grasping operation is one of the key issues.Grippers are used to grasp,carry,and place the target object,which are the main implementation form of robotic grasping operation actuators.For the mechanism design,the underactuated mechanism has well shape-adaption,of which the number of driving units are less than that of degrees of freedom.Due to the advantages of free assembly,free friction,as well as high precision,compliant mechanism becomes the main form of end actuators in the fields of precision engineering,bionic robot and so on.For the grasping control,the interactive security and operation reliability of robotic grasping mechanism under uncertainty can be further improved by designing the active control algorithm properly.Based on the background above,the design and control of self-adaptive compliant underactuated gripper are researched in this paper:(1)A novel compliant underactuated gripper with multi grasping modes is proposed by combining a rigid underactuated gripper,the compliant mechanism and the flexible material,which dedicates to improve the adaptability and generality of robotic grasping end-actuator.The gripper has two grasping modes,namely two-point grasping and enveloped grasping.Based on the pseudo-rigid-body method,static analysis of different working modes are carried out,establishing an analytical relationship between the output grasping forces and the input load.For the enveloped grasping mode,an algorithm determines the static equilibrium position is given.Furthermore,a multi-objective optimization algorithm of structural parameters based on gradient descent is designed to obtain the maximum grasping forces.The effectiveness of two grasping modes,grasping force models,and optimization algorithm are verified by a dynamic simulation package and finite element analysis.(2)A self-adaptive impedance control algorithm with the ability of switching the tracking modes automatically is proposed to control the novel compliant underactuated gripper for realizing the adaptive adjustment of force and position parameters in multi grasping mode operation under uncertainy.Utilizing the designed force sensor system which supplies the feedback signal to the control scheme,the measurement of grasping forces and the recognition of grasping modes are realized simultaneously.The kinematic models of compliant underactuated gripper are derived to establish the relationship between the grasping feed and the target position of motor rotor.Based on recursive least squares method and linear quadratic regulator,an optimal impedance control algorithm,which self-adaptively assigns the weight of tracking modes according to the evaluated stiffness of grasped object,is established.Then,the corresponding grasping control scheme with robust design is designed and verified by simulation.(3)Experimental studies are carried out to verify the proposed novel compliant underactuated gripper and optimized self-adaptive impedance control algorithm.For the gripper design,the corresponding gripper prototypes are designed and the force measurement equipment is constructed to verify the effectiveness of grasping force modeling and optimization algorithm.Various grasping experiments are conducted to further validate each working modes,the stability of grasping,and the ability to protect fragile objects.For the grasping control,an experimental system is constructed and a variety grasping control experiments are carried out to verify the advantages of control algorithm and the effectiveness of adaptive gripping control of two grasping modes.