| The number of "severely disabled" elderly and patients caused by a large number of accidents is increasing,which puts higher demands on nursing work.Nursing staff often need to help the long-term bedridden patients to prevent diseases such as pressure sores and help them carry out rehabilitation training on schedule.Therefore,studying a robot hand that imitate the human hand to grip and manipulate the human limbs to assist the nursing staff to work is of great significance for simplifying the mechanical structure of the existing nursing bed and studying humanoid with versatility and compact structure.Unlike other robot hands,the safety and comfort of the human's limbs when is gripped is the first consideration in the design and control of the robot hand.The main parameters affecting the safety and comfort are the stress and strain and the average stress and strain generated by gripping force inside the human's limbs.In this paper,the biomechanical method is used to analyze the biomechanical effect on the human's limbs under different gripping force,which provides theoretical guidance for the structure and joint control of the robot hand.In this paper,the 3D model of the human calf is reconstructed by MIMICS using the CT scan images and the model is processed,smoothly by Geomagic Studio.The finite element(FE)model of the calf model is established by HyperMesh and ABAQUS.The skin and bone of the FE model use linear elastic material,and the muscle adopts the Odgen hyperelastic material.In ABAQUS,muscle is connected with skin and bone by tie constraint.The contact algorithm between skin and the fingers of the robot hand adopts the surface-to-surface contact constraint algorithm.Next,use the lifting platform,pressure gauge and single-joint translation robot hand to exert pressure on the volunteer's calf,record the robot hand's displacement-pressure data and compare the data with the data obtained by simulation with the FE model to verify the validity and availability of the FE model.Then the FE model is used to analyze the stress and the strain generated by the single-joint robot hand when using different angles,force and friction coefficient to grip the calf model.Through the simulation experiment data,we find that it is more appropriate to grip the calf with an angle of about 50-60°.Compared with the single-joint translation robot hand,the two-joint robot hand has more flexible operability and its interaction with the calf model can produce a better envelope.This paper studies the biomechanical properties of the calf gripped by the two-joint robot hand and researches the effects of the gripping joint angle,the gripping position,the gaskets' material and the fingers' sizes of the robot hand on the stress and strain of the calf.The results show that the first joint angle and the second joint angle should be respectively 0° and 50°.The softer the gasket material,the smaller the stress and strain on the calf.Increasing the length of the second knuckle has obvious effect on reducing the stress and strain,while increasing the first knuckle has little effect.In this paper,the experiment results based on blood oxygenation index and subjective comfort evaluation are used to verify the simulation results of gripping the calf using the two-joint hand.The experiment based on blood oxygen index is to monitor the blood oxygenation saturation change of the calf before and after being gripping by the robot hand using the near-infrared tissue blood oxygenation monitor,and compares the results with simulation results to verify the correctness of the simulation analysis results.The subjective comfort evaluation is the evaluation of the volunteers when their calves are gripped and the results are compared with the simulation results to verify correctness of the simulation results and the research method.The research results in this paper can not only provide guidance for the structural design and control optimization of the nursing robot hand,but also provide a useful reference for studying and analyzing the impact of other similar robot hand gripping on the human limbs. |
PDF Full Text Request