Research On Mechanism And Slip Prevention Control Of A Dexterous Prosthetic Hand With Capabilities Of Manipulation And Perception

A prosthetic hand is a representative of the biomechatronic systems,which is interested in the physical and interaction performance integration between human and the mechatronic devices and is a new interdiscipline with fusion of the biological science.Although the appearance and the performance have been in some extent improved in resent years,the dexterity,the perception and the controllability of the prosthetic hand are limited due to the development of the motors and sensors.This paper focuses on the correlative technologies of the anthropomorphic dexterous prosthetic hands to improve the appearance,the dexterity,the perception,the controllability and the practicability.The main research contents include the configuration design,the mechanical design and the slip prevention control of the anthropomorphic prosthetic hands.This paper made a review about the state of the prosthetic hands from the point of view of a configuration design.Then a configuration design method of a prosthetic hand was proposed.It consists of two parts including the thumb configuration and the fingers layout on the palm.Firstly,the thumb functions of human hands are analyzed based on the anatomical model and the configuration characteristics of the thumbs for typical prosthetic hands are summarized.Then the thumb parameters are optimized based on the manipulability measure.On the basis of the thumb configuration analysis,a design method of the fingers layout on the palm is proposed based on form closure theory.To consider the two parts of measures synthetically,the optimization function is established and the configuration parameters are optimized based on the genetic algorithm.Multiple groups of grasp simulations have been used to validate the effectiveness.Considering anthropomorphism,dexterity,sensing,controllability and practicability,a 6-DOF modular and multisensory prosthetic hand was developed.The fingers are identical except the thumb.The finger internally integrated with the actuator,the sensors and the controller as a modular unit can realize the perception and control independently.It is easy to be fixed,maintained and applied to partial upper-limb amputees.The drive chain is optimized based on complex method,which aims to adjust the requirement of the actuators integrated in the fingers to reduce the mass of the finger.The self-locking ability can make the finger automatically continue holding an object in condition of power-off so as to extend the working time.The thumb is configured with the adduction/abduction motion to improve the grasping performance.Integrated with multiple sensors including the position,the torque and the tactile sensors measuring the force in three directions,the prosthetic hand can perceive the environment greatly.In addition,a cosmetic glove is designed to provide a durable cover that helps protect the hand and promote the application.When an object is grasped by the prosthetic hand,it may often slip because of the external disturbance.Consequently,a slip prevention control method was proposed based on the tactile feedback.It is composed of three stages including the initial stable grasp,the slip detection and the dynamic adjustment of the grasp force.Based on the grasp force applied on the objects with different stiffness from human hands,the relationship between the grasped objects and their desired force is established.The object stiffness estimation is realized with fusion of the position and tactile information and the corresponding desired force is given.The impedance control in cartesian space is applied to help achieve stable and compliant grasps,where PD robust controller based on the disturbance observer is used to compensate the unknown disturbance of the prosthetic hand so as to improve its inner position control accuracy.Based on the friction vibration theory and the discrete wavelet transform,the contact force is analyzed and the slips are real-time and accurately detected.Then the contact force is adjusted and controlled through the integral force increment resulted from the slips,which can real slip prevention without overlarge deformation.To validate the comprehensive performance of the prosthetic hand,many groups of experiments were designed.The system performance tests have shown that the prosthetic hand with a cosmesis still ensures the impedance characteristics and its force control accuracy.The slip prevention experiments have shown that the prosthetic hand can identify the grasped objects accurately,realize the contact compliance and the accurate force control.When the slips happen,the prosthetic hand can fast prevent them and protect the objects against the damage.The presented strategy has the advantages such as the strong real-time ability.The clinical experiments of the prosthetic hand show that the upper-limb amputee can achieve the dexterous manipulations for the typical grasp postures in our daily lives with a higher success rate and the grasp finishing time can meet the daily requirement,which indicates a good application prospect.