Design And Performance Evaluation Of Transradial Interface For Forearm Prosthetic Hand

Although the probability of upper-limb amputation is small,the overall number is large and still growing.What upper-limb amputees need most urgently is the reconstruction of lost motion functions and rehabilitation help.Transradial amputation level is the transverse loss of a part of the forearm,which is one of the upper-limb amputation levels.The forearm residual limb contacts with the prosthetic hand directly by the transradial prosthetic interface or socket,that is the “human(forearm residual limb)machine(prosthetic hand)interface”.In transradial prosthetic interface design,load related comfort and safety requirement contradicts with motion transfer related function requirement.To solve the problem of this contradiction,from the aspects of anatomy and physiology and prosthetic operation habits,combining with the engineering design approach,this paper aimed to design a frame-type transradial interface which meets comfort and safety and efficient motion transfer function requirements,as well as to propose corresponding biomechanical design methods and theories.Detailed research contents and conclusions are as follows:(1)The nonlinear viscoelastic biomechanical properties of transradial interface soft tissues under large deformation could be described by an adaptive QLV(Quasi-Linear Viscoelastic)model composed of three relaxation functions,and the safety design indicators could be obtained based on the adaptive QLV model theoretically.An incremental ramp-and-hold test,a single large amplitude ramp-and-hold test and a sinusoidal cyclic test at large strain amplitude were adopted in this study,results showed that the adaptive QLV model could predict these three kinds of load conditions,and the influence of loading strain rates on the adaptive QLV model was also analyzed.Based on the adaptive QLV model and the strain-time cell-death threshold for skeletal muscle,the safety indicators of forearm soft tissues were theoretically analyzed.That is,the maximum compression stress and the maximum compression engineering strain were 186.7 kPa and 0.411,respectively.(2)The concept of “regional load-bearing to control the underlying residual bone” was proposed to a frame-type transradial prosthetic interface;regional differences in pain threshold of normal human forearms and loading areas selection were studied.Regional differences in pain threshold could be evaluated using PPT(Pressure Pain Threshold)and DPT(Deformation pain threshold),average PPT contour maps and average DPT contour maps of left and right forearms for all subjects could be selected as design references for comfort and motion transfer function design of transradial interface.Based on the proposed load-bearing selection criteria and the average PPT contour maps,we selected a load-bearing scheme for medium transradial interface with four loading areas,and two schemes for long transradial interface with six loading areas were also selected.(3)It was proposed that switching chambers between tight and relax statues to achieve function and comfort and safety of the load-bearing areas.The distance design approach of the chamber was proposed,the compression theory of the chamber with negative characteristics was proposed and the structure design method was also proposed.The distance of chambers in the medium transradial interface was set as H*(0.106,0.159),and the distance of chambers in the long transradial interface was set as H*(0.0725,0.1084),H was the thickness of the soft tissues in the load-bearing areas.The power consumption of the chamber with negative characteristics was lower than the chamber's with positive characteristics.The range value of the chamber's negative stiffness was theoretically set to-7.1 N/m-0,the stiffness coefficient of the leaf spring was set to-2.9688 N/mm,a single chamber was composed of four leaf springs and six coil springs,the experimental stiffness coefficient of the chamber was-7 N/mm.Based on these theories,the 3D models of medium and long transradial interface were designed,respectively.(4)The concept of “controlling chambers' status on load-bearing areas according to time” was proposed,biomechanical analysis of each chamber's status was carried out in different gesture modes of the transradial interface system,and the corresponding control system was also designed.The four chambers in the medium transradial interface were suggested to being in tight or relax statues together to lift load-bearing ability and comfort and to simplify the control system.Scheme A of the long transradial interface had the largest number of chambers in relax status in flat gesture with thumb lateral,scheme B of the long transradial interface had the largest number of chambers in relax status in flat gesture with thumb forward,scheme A was superior than scheme B under heavy load conditions.The chambers' statues in different gesture modes were controlled by corresponding control system,the accuracy of attitude angle was improved by explicit complementary filter algorithm of the accelerator and gyroscope's data confusion,and the upper PC software was also designed.(5)Physical designs and performance evaluations of the medium transradial interface with four chambers,and two schemes of the long transradial interfaces with six chambers were also carried out.The medium transradial interface was better than fixed frame-type prosthetic interface in function and comfort,for long transradial interface schemes,the performance of scheme A was better than the performance of scheme B,scheme A was suggested for the long residual limb condition.That is,four load-bearing areas in the proximal of the forearm,and two load-bearing areas in the anterior and posterior of the distal of the forearm.In this paper,an adaptive QLV biomechanical model was proposed to describe the nonlinear viscoelastic biomechanical properties of transradial interface soft tissues under large deformation,the concepts of “regional load-bearing to control the underlying residual bone” and “controlling chambers' statuses according to time” were proposed to design the frame-type transradial interface,average PPT counter maps and average DPT counter maps and load-bearing areas selection criteria were proposed,the theory of the chamber's distance and negative stiffness characteristics and the corresponding structure design methods were also introduced,based on biomechanical studies of gesture modes of transradial interface,the corresponding hardware and software control system were also designed.Based on these proposed methods and theories,the medium and long transradial interfaces were designed respectively,it proved that the comfort and safety and efficient motion transfer function requirements were achieved,and it also proved that the load related problem of the contradiction of transradial prosthetic interface was solved in a certain degree.