Research On Design And Functional Integration Of Electro-hydraulic Lower Limb Prostheses

Lower limb prostheses are crucial devices for above-knee amputees to regain mobility and independence.The development of high-performance lower limb prostheses is of paramount importance in enhancing the quality of life for amputees while also alleviating the burden on society.Lower limb prostheses are divided into passive prostheses or powered prostheses,depending on their capacity to generate torque actively.The passive knee prostheses follow the movement of the residual limb compliantly,but they lack active torque.The powered knee prostheses generate active torque and have more motion modes,yet the balance between free joint swing,low weight and large torque output cannot be achieved due to the incompatibility between low passive friction and high active transmission ratio in their drive system.In addition,biomechanical studies have demonstrated the presence of significant inter-joint synergistic movements and energy transfer in the knee and ankle joints of human lower limbs during walking.However,most knee-ankle prostheses are powered by a motorized knee with a motorized ankle that only focuses on inter-joint synergistic motion while neglecting inter-joint energy transfer,resulting in excessive energy consumption at the ankle joint in such prostheses.Although a few knee-ankle prostheses are equipped with energy transfer mechanisms,their structures are complex and subject to motion interference,rendering them impractical for use.In light of the limitations of current lower limb prostheses,this paper aims to overcome the key challenges associated with electro-hydraulic lower limb prostheses,including drive principle design,prosthesis system integration,patient wear testing and analysis based on biomechanical principles governing human lower limb joints.The main research contents and conclusions are presented below:(1)The bionic design methods of lower limb prostheses were proposed.We analyzed the requirements for prosthetic use among amputees with different mobility,and have developed a multi-rigid body motion model as well as an inverse kinematic model of the human lower limbs to establish a theoretical foundation for the design,testing,and analysis of lower limb prostheses.The biomechanical characteristics of the lower limb joint movements were analyzed,and the bionic design principles and functional requirements of the knee and knee-ankle prostheses were proposed,which provided the theoretical basis for the bionic design of the lower limb prosthesis structure and drive system.(2)An electro-hydraulic powered knee prosthesis was designed and optimized.In order to solve the current difficult compatibility problems in driving powered knee prosthesis,an electro-hydraulic powered knee prosthesis(EHPK-1)with a hybrid active-passive integrated drive scheme was proposed,and rapid development and proof-of-principle were achieved by using commercially available hydraulic components.Based on the EHPK-1 drive system,we continued to design the electrohydraulic powered knee prosthesis(EHPK-2),optimized the structure of the electrohydraulic drive system,reached a maximum transmission ratio of 174:1,improved the sensing and control system,and realized the integration of the EHPK-2 knee prosthesis.(3)Performance testing and analysis of the electro-hydraulic powered knee prosthesis were carried out.The minimum damping force of EHPK-2 drive system was3 N and the passive extension torque was 4.42 Nm,which is better than the same type of knee prostheses.Motion testing of amputees was conducted to evaluate the performance of the EHPK-2 in terms of gait symmetry,joint angles and toruqes.The maximum flexion angle in level walking was about 60°,and the peak output torque in stair ascent was greater than 60 Nm.This indicates that the EHPK-2 has the flexibility of a passive prosthesis,the swing stability of an active prosthesis,and sufficient torque output of an active prosthesis,solving the incompatibility between low passive friction and high transmission ratio of powered knee prostheses.(4)The design methods and functional integration of an electro-hydraulic powered knee-ankle prosthesis were developed.To address the problems of lack of inter-joint energy transfer and high energy consumption of the ankle joint of the prosthesis,based on the synergistic motion and energy transfer mechanism between the human knee and ankle joint,the electro-hydraulic powered knee-ankle integrated prosthesis(EHPKA)is proposed as a hybrid active-passive drive principle,and three drive schemes are designed for linkage,non-linkage and independent work.The modular design method of knee and ankle integrated prosthesis was proposed,and the EHPKA system integration was completed,in which the weight of knee and ankle joints were 2.23 kg and 1.09 kg,respectively.the EHPKA realized the inter-joint energy transmission,which made the prosthesis with the advantages of light weight,high integration and wide adaptability.The level walking controller was developed for different working modes.To shorten the commissioning time of the prosthesis,a prosthetic motion control APP was designed.(5)The wearing testing of the electro-hydraulic knee-ankle prosthesis was carried out.Tests of amputee motion and energy metabolism were conducted in a horizontal walking environment with an electro-hydraulic knee-ankle integrated prosthesis in knee-ankle linkage and non-linkage modes.The results showed that with knee-ankle linkage,the EHPKA prosthesis improved the locomotor gait on the amputee side,with a 7.5% increase in peak ground reaction force and a 5.8% reduction in the effective value of the hip moment.In addition,the EHPKA reduced the patient’s metabolic cost,with a 4.0% reduction in oxygen consumption and a 3.3% reduction in energy expenditure rate.The ankle joint electrical energy consumption was only 2.6 W.The EHPKA was verified to have good stable support performance under different slopes by slope standing test.In summary,the electro-hydraulic active-passive integrated drive principle of the knee prosthesis proposed in this paper solved the difficult compatibility between low passive friction and high active transmission ratio of knee prostheses,and realized the integrated integration of joint free swing and large torque active drive.The activepassive hybrid drive principle and modular design method of the knee-ankle integrated prosthesis proposed in this paper solved the problem of lack of energy transmission between the joints of knee-ankle prostheses and high energy consumption of the ankle joint of the prostheses,while enhancing the adaptability and comfort of the prostheses.